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Flashcards in C5 - Quantitative Analysis Deck (44)
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1

What is the formula of sulfuric acid?

H2SO4

2

What is the formula of nitric acid?

HNO3

3

What is the formula of sodium hydroxide?

NaOH

4

What is the formula of sodium sulfate?

Na2SO4

5

What is the formula of lead (II) nitrate?

Pb(NO3)2

6

What is the formula of lead iodide?

PbI2

7

What is the formula of potassium iodide?

KI

8

What is the formula of potassium nitrate?

KNO3

9

What is a substance's molar mass?

It's relative molecular mass is equal to it's molar mass.

10

How would you calculate the number of moles a substance has?

number of moles = mass / molar mass

11

What is the relative atomic mass of an element?

The average mass of the atom of an element compared to the average mass of 1/12th of a carbon-12 atom.

12

1dm= ?

1dm3 = 1000 cm3

13

What is the equation for concentration in terms of moles and volume?

amount in moles = concentration x volume

14

Why is the amount of NaCl (sodium chloride) not always an accurate reflection of the amount of sodium in a certain food substance?

Sodium ions may derive from sources other than NaCl.

15

Describe the steps in a simple acid-base titration.

- Acid in burette, alkali in flask.

- Acid slowly added to alkali until end point is reached.

- We know when we've reached the end point because of a sudden change in colour caused by the pH indicator.

16

Why do titrations needed to be carried out several times?

1. Firstly, a rough titration is done to get an approximate idea of how much acid/alkali is needed to neutralise.
2. Further titrations are then carried to get a more accurate figure.
3. Experiment then repeated to ensure reliability of results.

17

Explain why an acid-base titration should use a single indicator rather than a mixed indicator

A single indicator changes colour suddenly/immediately when the pH reaches a certain threshold. This allows the end point to be identified. On the other hand, mixed indicators change colour gradually - meaning the end point can't be accurately identified.

18

Why is the amount of product produced in a reaction directly proportional to the amount of limiting reactant used?

If you increase the amount of limiting reactant, you're increasing the number of particles that will be reacting. Therefore, you increase the amount of product produced (since more particles will react with each other to produce product).

19

How can a reversible reaction reach an equilibrium?

1. The forward reaction (reactants being turned into products)  slows down as the concentration of the reactants falls.

2. The backward reaction (products turning back into original reactants) speeds up as the concentration of the products increases.

3. Eventually, the rate of the forward reaction will equal the backward reaction, this is the point of equilibrium.

4. At this point, the concentrations of products and reactants are constant and do not change.

20

Why is a closed system needed for an equilibrium?

A closed system is needed for an equilibrium so that products or reactions do not escape.

21

How does increasing the concentration of the reactants change the position of the equilibrium?

When you increase the concentration of the reactants, the equilibrium tries to the correct this by shifting toward the right. In other words, it attempts to reduce the concentration of the reactants by turning more of them into products.

22

How does increasing the concentration of products change the position of equilibrium?

If you increase the concentration of the products, the equilibrium moves to the left. This is because it tries to 'balance' the reaction by reducing the concentration of products through increasing the rate of the backward reaction. 

23

How does increasing the pressure change the position of equilibrium in a reaction involving gases.

If you increase the pressure, the equilibrium tries to reduce the pressure by moving in the direction where there are fewer moles of gas. 

24

How does decreasing the pressure change the position of equilibrium in a reaction involving gases?

If you decrease the pressure, the equilibrium tries to increase the pressure by moving in the direction where there are more moles of gas. 

25

How does increasing the temperature change the position of equilibrium?

If you increase the temperature, the equilibrium will try and decrease the temperature by moving in the endothermic direction.

26

How does decreasing the temperature change the position of equilibrium?

If you decrease the temperature, the equilibrium will try and raise the equilibrium by moving in the exothermic direction.

27

Describe the three main stages in the Contact Process.

1. Sulfur is burnt to produce sulfur dioxide.

2. Sulfur dioxide reacts (in a reversible reaction) to produce sulfur trioxide.

3. Sulfur trioxide reacts with water to produce sulfuric acid.

28

What is the word equation for the reaction between sulfur dioxide and oxygen?

sulfur dioxide + oxygen  ⇌ sulfur trioxide

29

What are the conditions used in the contact process?

1. V2O(vanadium pentoxide) catalyst

2. Temperature of around 450 degrees
3. Atmospheric pressure

30

Why is a temperature of 450 degrees used in the contact process?

Increasing the temperature moves the equilibrium toward the left, so ideally it needs to be as low as possible. However, increasing the temperature also increases the rate of reaction. Therefore, a compromise is chosen between rate of reaction and equilibrium position. 450 degrees is that compromise.