topic 3 - quantitative chemistry

Question 1

What is the law of conservation of mass?

Answer 1

The law of conservation of mass states that no atoms are lost or made during a chemical reaction meaning the mass of the products is equal to the mass of the reactants.

Question 2

What is required for a chemical equation to be balanced?

Answer 2

A balanced chemical equation must have the same number of atoms of each element on both the reactant side and the product side.

Question 3

How do you calculate the relative formula mass (Mr) of a compound?

Answer 3

The relative formula mass (Mr) of a compound is calculated by summing the relative atomic masses of all atoms in the compound as indicated by the formula.

Question 4

Calculate the Mr of HCl (Hydrochloric acid).

Answer 4

For HCl the Mr is calculated as follows: H = 1 Cl = 35.5. Therefore Mr = 1 + 35.5 = 36.5.

Question 5

What can be inferred about mass in a balanced chemical equation?

Answer 5

In a balanced chemical equation the sum of the Mr of the reactants is equal to the sum of the Mr of the products indicating that no mass is lost during a reaction.

Question 6

What happens to mass when a reactant or product is a gas?

Answer 6

Mass changes can occur if a reactant or product is a gas particularly if gas is allowed to escape during a reaction which can lead to a measured mass loss.

Question 7

Describe a scenario where the conservation of mass may appear to be violated during a reaction. How can this be explained?

Answer 7

A common scenario is when a gas is produced in a reaction or a gas is consumed. If the gas escapes from a closed system it may appear that mass was lost; however if all products and reactants are accounted for the total mass would remain the same.

Question 8

How can you demonstrate that the mass is conserved in a chemical reaction?

Answer 8

To demonstrate mass conservation you can conduct a reaction in a closed container measure the mass before and after the reaction and show that the mass before (reactants) equals the mass after (products).

Question 9

What topics are related to quantitative chemistry in GCSE Chemistry?

Answer 9

Related topics include stoichiometry empirical and molecular formulas concentration calculations titration calculations and gas laws.

Question 10

Why is it important to balance chemical equations?

Answer 10

Balancing chemical equations is crucial because it ensures that the law of conservation of mass is upheld provides accurate stoichiometric ratios for reactions and is essential for calculating yields and concentrations.

Question 11

What should be considered when observing a change in mass during a reaction?

Answer 11

Check whether the change in mass is due to a reactant or a product particularly if the substance involved is a gas that may have been released into the atmosphere.

Question 12

Provide an example of a reaction involving a change in mass.

Answer 12

When a metal reacts with oxygen the mass of the metal oxide product may differ from the mass of the original metal due to oxygen being added to form the oxide.

Question 13

What is an important consideration regarding chemical measurements?

Answer 13

Whenever a measurement is made there is always some uncertainty associated with the result obtained.

Question 14

What is the importance of estimating uncertainty in chemical measurements?

Answer 14

Estimation of uncertainty is important because it provides a range of values that accounts for possible errors in the measurement process.

Question 15

What unit is used to measure chemical amounts?

Answer 15

Chemical amounts are measured in moles with the symbol for the unit being ‘mol’.

Question 16

What does the mass of one mole of a substance in grams equal?

Answer 16

The mass of one mole of a substance in grams is numerically equal to its relative formula mass (Mr).

Question 17

What is the relative formula mass (Mr) of iron and what is the mass of one mole of iron?

Answer 17

The Mr of iron is 56 so one mole of iron weighs 56g.

Question 18

What is the relative formula mass (Mr) of nitrogen gas (N2) and what is the mass of one mole of nitrogen gas?

Answer 18

The Mr of nitrogen gas (N2) is 28 (calculated as 2 x 14) so one mole of nitrogen gas weighs 28g.

Question 19

What does one mole of a substance contain in terms of particles?

Answer 19

One mole of any substance contains Avogadro’s number of particles which is approximately 6.022 x 10²³ particles.

Question 20

What topic is referred to when discussing the calculation of moles in relation to the masses of pure substances?

Answer 20

This topic is referred to as ‘Quantitative Chemistry’.

Question 21

What is the higher tier content noted in the AQA GCSE Chemistry syllabus?

Answer 21

The content in bold is designated for Higher Tier students indicating advanced topics within the syllabus.

Question 22

What role does the gas released play in chemical reactions and mass change observations?

Answer 22

If a gas is released during a chemical reaction its mass is not taken into account in the total mass change leading to an apparent decrease in mass.

Question 23

Why is it necessary to understand moles in quantitative chemistry?

Answer 23

Understanding moles is essential for performing stoichiometric calculations determining yields and converting between mass and number of particles in chemical reactions.

Question 24

What is the definition of a mole in chemistry?

Answer 24

A mole is a unit of measurement used to express amounts of a chemical substance. One mole contains exactly 6.022 x 10^23 particles which may be atoms molecules ions or other entities.

Question 25

What is Avogadro's constant?

Answer 25

Avogadro's constant is 6.022 x 10^23 particles per mole. It is the number of atoms molecules or ions in one mole of a substance.

Question 26

How do you convert between mass and moles?

Answer 26

You can convert between mass and moles using the formula: Moles = Mass / Molar Mass where molar mass is the mass in grams of one mole of a substance. Alternatively you can use a triangle where Mass is on top and Moles and Molar Mass are on the bottom.

Question 27

Given 42g of carbon (C) how many moles are there?

Answer 27

To calculate the moles use the formula Moles = Mass / Molar Mass. The molar mass of carbon is approximately 12g/mol. Thus Moles = 42g / 12g/mol = 3.5 moles.

Question 28

What does the chemical equation Mg + 2HCl → MgCl2 + H2 represent?

Answer 28

This chemical equation indicates that 1 mole of magnesium (Mg) reacts with 2 moles of hydrochloric acid (HCl) to produce 1 mole of magnesium chloride (MgCl2) and 1 mole of hydrogen gas (H2).

Question 29

What is the law of conservation of mass in relation to chemical equations?

Answer 29

The law of conservation of mass states that the total mass of reactants must equal the total mass of products in a chemical reaction. Therefore the total number of moles of each element must be the same on both sides of a balanced chemical equation.

Question 30

How can you balance chemical equations using moles?

Answer 30

To balance chemical equations using moles follow these steps: a. Convert the masses of reactants and products to moles using their respective molar masses. b. Adjust coefficients in front of the chemical formulas to ensure the number of moles of each element is equal on both sides of the equation.

Question 31

What are the steps to calculate masses of reactants and products from balanced equations?

Answer 31

1. Write the balanced chemical equation. 2. Determine the number of moles of the known substance. 3. Use the mole ratio from the balanced equation to find moles of other substances. 4. Convert moles back to grams using molar masses as necessary.

Question 32

In the reaction between magnesium and hydrochloric acid if 3.5 moles of Mg are used how many moles of HCl are needed?

Answer 32

According to the balanced equation 1 mole of Mg reacts with 2 moles of HCl. Therefore for 3.5 moles of Mg you need 3.5 moles × 2 = 7 moles of HCl.

Question 33

What role does molar mass play in converting between grams and moles?

Answer 33

Molar mass is a conversion factor that relates the mass of a substance (in grams) to the number of moles. It is defined as the mass of one mole of a substance typically expressed in grams per mole (g/mol).

Question 34

What is a simple whole number ratio in the context of moles of elements or compounds?

Answer 34

A simple whole number ratio indicates the relative amounts of moles of different elements or compounds involved in a chemical reaction representing their proportional relationship in the reaction.

Question 35

What is a limiting reactant?

Answer 35

The limiting reactant is the reactant that is completely consumed in a chemical reaction determining the maximum amount of product that can be formed.

Question 36

Why is it important to identify the limiting reactant in a reaction?

Answer 36

Identifying the limiting reactant is crucial because it dictates the extent of the reaction and the amount of product that can be produced. It ensures that calculations for product formation are based on the reactant that runs out first.

Question 37

If a reaction has one reactant in excess how does that affect product formation?

Answer 37

When one reactant is in excess the amount of product formed is entirely dictated by the amount of the limiting reactant as the excess reactant will not affect the final amount of product produced.

Question 38

What is the equation used to calculate the mass of solute in a solution given its concentration and volume?

Answer 38

The mass of solute can be calculated using the formula: mass (g) = concentration (g/dm³) x volume (dm³).

Question 39

How does a smaller volume or larger mass of solute affect concentration?

Answer 39

A smaller volume or a larger mass of solute increases the concentration of the solution resulting in a higher grams per dm³ (g/dm³) value.

Question 40

How does a larger volume or smaller mass of solute affect concentration?

Answer 40

A larger volume or a smaller mass of solute decreases the concentration of the solution resulting in a lower grams per dm³ (g/dm³) value.

Question 41

What measurement units are typically used for concentration of solutions?

Answer 41

Concentration of solutions is typically measured in grams per cubic decimeter (g/dm³) or moles per liter (mol/L).

Question 42

Explain the significance of knowing both the concentration and volume of a solution in practical applications.

Answer 42

Knowing both the concentration and volume of a solution is essential for calculating the amount of solute present which is crucial for preparing solutions of desired concentrations performing reactions with correct stoichiometry and ensuring accurate results in laboratory experiments.

Question 43

What happens to the amount of product produced if the limiting reactant is used in calculations?

Answer 43

When the limiting reactant is used in calculations the amount of product produced is directly proportional to the amount of the limiting reactant that is consumed. This reflects the maximum yield based on the stoichiometry of the reaction.

Question 44

What is the formula for calculating percentage yield?

Answer 44

Percentage Yield = (Amount of product produced / Maximum amount of product possible) x 100

Question 45

Why is it not always possible to obtain the calculated amount of a product in a chemical reaction?

Answer 45

There are three main reasons: 1. The reaction may not go to completion because it is reversible. 2. Some of the product may be lost when it is separated from the reaction mixture. 3. Some of the reactants may react in ways different from the expected reaction.

Question 46

Define 'yield' in the context of a chemical reaction.

Answer 46

Yield is the amount of product obtained from a chemical reaction.

Question 47

How do you calculate the theoretical mass of a product from a given mass of reactant?

Answer 47

1. Calculate the moles of reactant using the molar mass. 2. Use the balancing numbers from the balanced equation to find the moles of product. 3. Calculate the theoretical mass of the product.

Question 48

If you have 2 moles of HCl how many moles of MgCl2 would be produced in the reaction 2HCl + Mg -> MgCl2 + H2?

Answer 48

You would divide the moles of HCl by 2 resulting in 1 mole of MgCl2.

Question 49

What is meant by 'theoretical mass'?

Answer 49

The theoretical mass is the mass of product that could be formed from given reactants according to the stoichiometric calculations based on the balanced chemical equation.

Question 50

What are three factors that can reduce the percent yield of a reaction?

Answer 50

1. Incomplete reaction due to reversibility. 2. Loss of product during separation. 3. Unanticipated side reactions of reactants.

Question 51

Explain the significance of balancing equations in stoichiometry.

Answer 51

Balancing equations is crucial because it ensures that the number of atoms for each element is conserved across the reactants and products allowing accurate stoichiometric calculations of reactants and products.

Question 52

How would you determine the molar mass of a substance?

Answer 52

The molar mass of a substance can be determined by adding up the atomic masses of each element in the chemical formula of the substance based on the periodic table.

Question 53

What is atom economy and why is it important?

Answer 53

Atom economy measures the proportion of reactants that become useful products which is important for assessing the efficiency of a chemical reaction and minimizing waste in chemical processes.

Question 54

List three reasons why atom economy is a significant consideration in green chemistry.

Answer 54

1. It helps to reduce environmental impact by minimizing waste. 2. It promotes the use of resources more efficiently. 3. It fosters sustainable practices by encouraging the development of reactions that yield more desired products.

Question 55

What is atom economy?

Answer 55

Atom economy is a measure of the amount of starting materials that end up as useful products in a chemical reaction. It is important for sustainable development and economic reasons as reactions with high atom economy are preferred.

Question 56

How is atom economy calculated?

Answer 56

Atom economy is calculated using the formula: (Mr of desired product from reaction / Sum of Mr of all reactants) x 100.

Question 57

What factors influence the choice of a particular reaction pathway?

Answer 57

Factors influencing the choice of a reaction pathway include atom economy yield reaction rate equilibrium position and the usefulness of any by-products.

Question 58

What is the relationship between the mass of a solute volume of a solution and concentration?

Answer 58

The mass of a solute and the volume of a solution are related to the concentration of the solution through the equation: Concentration = Moles of solute / Volume of solution (in dm³).

Question 59

How do you calculate moles from mass and molar mass?

Answer 59

Moles can be calculated using the formula: Moles = Mass (g) / Molar Mass (g/mol).

Question 60

What units are used to measure concentration in chemistry?

Answer 60

Concentration can be measured in moles per given volume of solution typically expressed as mol/dm³.

Question 61

If the concentration of a solution is 3 mol/dm³ what does this mean?

Answer 61

A concentration of 3 mol/dm³ means that there are 3 moles of solute in every 1 dm³ (1000 cm³) of solution.

Question 62

What is the formula to relate concentration moles and volume?

Answer 62

The formula to relate these quantities is: Moles = Concentration (mol/dm³) x Volume (dm³).

Question 63

What does 'Higher Tier only' content refer to in chemistry notes?

Answer 63

'Higher Tier only' content refers to the advanced topics or equations that are included in the syllabus for students taking higher-level examinations in chemistry.

Question 64

What is the significance of equilibrium position in chemical reactions?

Answer 64

The equilibrium position determines the relative amounts of reactants and products present at equilibrium and influences the yield of the desired product in a chemical reaction.

Question 65

How can by-products be useful in a chemical reaction?

Answer 65

By-products can be useful if they can be separated and sold for profit or further utilized in other processes making the overall process more economically viable.

Question 66

What is the importance of yield in a chemical reaction?

Answer 66

Yield is important because it measures the efficiency of a reaction indicating how much of the desired product is obtained from the reactants.

Question 67

What are solutions that react completely called?

Answer 67

Solutions that react completely are referred to as 'stoichiometric solutions'. In a stoichiometric reaction all reactants are consumed to form products.

Question 68

How can the concentration of one solution be calculated when the concentration of the other is known?

Answer 68

The concentration of the second solution can be calculated using the mole ratio from the balanced chemical equation and the known moles of the first solution.

Question 69

How do you calculate the number of moles of a solution?

Answer 69

To calculate the number of moles of a solution use the formula: Moles = Concentration (mol/dm³) × Volume (dm³). Make sure the volume is converted to dm³ (1 dm³ = 1000 cm³).

Question 70

How do you convert volume from cm³ to dm³?

Answer 70

To convert volume from cm³ to dm³ divide the volume in cm³ by 1000. For example 500 cm³ is equivalent to 0.5 dm³.

Question 71

What is the equation to calculate the number of moles from volume and concentration?

Answer 71

The equation is: Moles = Concentration (mol/dm³) × Volume (dm³). This allows you to determine the amount of substance present in moles.

Question 72

How to calculate the concentration of an unknown solution?

Answer 72

To calculate the concentration of an unknown solution use the formula: Concentration (mol/dm³) = Moles / Volume (dm³). Moles can be determined from the mole ratio based on the stoichiometry of the reaction.

Question 73

What is the relationship between moles of gas and volume under the same conditions?

Answer 73

Under the same conditions of temperature and pressure equal amounts (in moles) of different gases occupy the same volume.

Question 74

What is the volume occupied by 1 mole of any gas at room temperature and pressure (RTP)?

Answer 74

At room temperature and pressure (20 degrees C and 1 atmosphere) 1 mole of any gas occupies 24 dm³.

Question 75

What is the formula to calculate volume of gas at RTP in terms of moles?

Answer 75

The formula is: Volume of gas (dm³) = Moles × 24. This relates the volume of a gas at RTP to the number of moles.

Question 76

What conditions define room temperature and pressure (RTP)?

Answer 76

Room temperature and pressure (RTP) are commonly defined as 20 degrees Celsius (°C) and 1 atmosphere (atm) pressure.

Question 77

What is quantitative chemistry concerned with?

Answer 77

Quantitative chemistry is concerned with measuring the quantities of reactants and products in chemical reactions often involving calculations of moles concentrations and volumes.

Question 78

What is a mole ratio and how is it used?

Answer 78

A mole ratio is derived from the coefficients of a balanced chemical equation showing the ratio of moles of reactants to moles of products. It is used to calculate the moles of one substance based on the moles of another in a reaction.

Question 79

What does RTP stand for in chemistry?

Answer 79

RTP stands for Room Temperature and Pressure which is typically defined as 20-25 degrees Celsius and 1 atmosphere of pressure.

Question 80

What is the equation to calculate the volume of a gas produced at RTP?

Answer 80

At Room Temperature and Pressure (RTP) the volume (in dm³) of a gas produced can be calculated by multiplying the moles of gas produced by 24 dm³. The formula is: Volume = moles x 24 dm³.

Question 81

If 5 moles of hydrogen gas are produced what is the volume of hydrogen gas produced at RTP?

Answer 81

If 5 moles of hydrogen gas are produced then the volume produced at RTP would be: Volume = 5 moles x 24 dm³ = 120 dm³.

Question 82

Why do we use 24 dm³ for calculating the volume of gas at RTP?

Answer 82

We use 24 dm³ for calculating the volume of gas at RTP because under these conditions 1 mole of an ideal gas occupies approximately 24 dm³.

Question 83

What is the importance of the gas constant in relation to gas laws?

Answer 83

The gas constant (R) is important in gas laws because it relates pressure volume and temperature of an ideal gas in equations such as the Ideal Gas Law (PV = nRT) where P is pressure V is volume n is moles of gas T is temperature and R is the gas constant.

Question 84

What is the Ideal Gas Law equation?

Answer 84

The Ideal Gas Law is represented by the equation: PV = nRT where P is the pressure of the gas V is the volume of the gas n is the number of moles of the gas R is the gas constant and T is the temperature in Kelvin.

Question 85

How do you convert temperature from Celsius to Kelvin?

Answer 85

To convert temperature from degrees Celsius to Kelvin you add 273.15. The formula is: K = °C + 273.15.

Question 86

What relationship does the Ideal Gas Law describe?

Answer 86

The Ideal Gas Law describes the relationship between pressure volume temperature and the amount of gas in moles for ideal gases allowing for the prediction of the state of a gas based on changes in these variables.

Question 87

In the context of gas calculations what does 'dm³' stand for?

Answer 87

In gas calculations 'dm³' stands for cubic decimeters which is a unit of volume equivalent to 1 liter.

Question 88

What assumptions are made when using the Ideal Gas Law?

Answer 88

When using the Ideal Gas Law it is assumed that the gas behaves ideally meaning that the gas particles have no volume and do not experience intermolecular forces. This assumption holds true for many gases under a wide range of conditions but deviations can occur at high pressures and low temperatures.