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Chemistry > CHEMICAL CALCULATIONS > Flashcards

CHEMICAL CALCULATIONS Flashcards

1
Q

What is the avogadro constant?

A

6.02 x 10*23 per mole

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2
Q

What is the equation for the number of moles?

A

Number of moles = mass/relative formula mass

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3
Q

What is the limiting reactant?

A

The reactant that gets used up first in a reaction is called the limiting reaction.

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4
Q

What is the equation for percentage yield?

A

Percentage yield = (actual mass of product produced / maximum theoretical mass of product possible) x 100

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5
Q

What factors affect percentage yield?

A

The reaction may be reversible
Some reactants may give an unexpected or unwanted product in alternative reactions.
Some products may be lost in the handling or left in the apparatus.
The reactants may not be pure.
Some of the desired product may be lost during its separation from the reaction mixture.

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6
Q

What is the equation for atom economy?

A

Percentage atom economy = (relative formula mass of the desired product from equation / sum of the relative formula masses of the reactants from the equations) x 100.

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7
Q

What is the equation for concentration when the volume is measured in dm*3?

A

Concentration (g/dm3) = amount of solute (g) / volume of solution (dm3)

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8
Q

How do you calculate the concentration of the volume of the solution is measured in cm*3?

A

Concentration = (amount of solution (g) / volume of solution (cm*3)) x100

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9
Q

Explain titrations.

A

Titrations are used to measure exact volumes of acid and alkali needed to react with each other.
Measure a known volume of alkali into a conical flask using a volumetric pipette.
Add a few drops of acid/base indicator to the solution in the conical flask and swirl.
Rinse a burette with distilled water, and then with some of the acid, allowing some acid to run through the tap. Then pour the acid you are going to use into the burette.
Record the reading on the burette. Then open the tap to release a small amount of acid into a flask. Swirl the flask to make sure that the two solutions are mixed.
Keep on adding the small amounts of acid until the indicator changes colour. Record the reading on the burette and work out the volume of acid that has run into the flask. This volume is known as a titre.
Repeat the whole process at least three times and discard any anomalous results. Or keep repeating until you get two results within 0.1cm*3 of each other. These precise results are called concordant.

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10
Q

What is the equation for the number of moles in a gas?

A

Number of moles in a gas = volume of gas (dm3) / 24 dm3

Number of moles in a gas = volume of gas (cm3) / 24 000 cm3

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11
Q

What is a mole?

A

One mole is simply the relative atomic mass of relative formula mass of any substance expressed in grams.
A mole of any substance will always contain the same number of atoms, molecules, or ions. This is a huge number called the avogadro constant (6.02 x 10*23]

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12
Q

What is the equation for the number of moles?

A

Number of moles = mass / atomic mass or relative formula mass.

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13
Q

What is the stoichiometry of the reaction?

A

The ratio of the number of moles of each reactant and product.

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14
Q

What is the yield of a reaction?

A

The mass of the product that a chemical produces is called its yield.

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15
Q

What is the percentage yield?

A

This compares the mass of product that the reaction actually produces with the maximum theoretical mass that it could possibly produce, as predicted from the balanced symbol equation.
The maximum mass possible is known as the theoretical yield of a reaction.

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16
Q

What is the formula for percentage yield?

A

Percentage yield = actual mass of product produced / maximum theoretical mass of product possible.
X 100

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17
Q

What factors affect percentage yield?

A

The reaction may be reversible.
Some reactants may react to give unexpected or unwanted products in alternative reactions.
Some of the products may be lost in handling or left in the apparatus.
The reactants may not be pure (as in the case if the lime kiln)
Some of the desired product may be lost during its separation from the reaction mixture.

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18
Q

What is the atom economy?

A

The atom economy of a reaction is a measure of the extent to which the atoms in the starting materials (the reactants) end up in the desired product. Any remaining atoms end up in the other products.

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19
Q

Hw do you calculate atom economy?

A

Percentage atom economy = relative formula mass of the desired product from equation / sum of the relative formula masses of the reactants from equation
X 100

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20
Q

How do you calculate the concentration of a solution?

A

Concentration (g/dm3) = amount of solute (g) / volume of solution (dm*3).

Concentration (g/dm3) = amount of solute (g) / volume of solution (cm3) x 1000.

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21
Q

Why might you carry out a titration?

A

To measure the exact volumes of acid and alkali needed to react with each other to form a neutral solution.

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22
Q

What is the end point of a titration reaction?

A

The point at which the acid and alkali have reacted completely is called the end point of the reaction. You judge when the end point is reached by using an acid/base indicator.

23
Q

What is the first step when carrying it a titration?

A

Measure a known volume of alkali into a conical flask using a volumetric pipette. First wash the pipette with distilled water then with some of the alkali.

24
Q

What is the second step when carrying it a titration?

A

Add a few drops of acid/base indicator to the solution in the conical flask and swirl.

25
Q

What is the third step when carrying it a titration?

A

Rinse a burette with distilled water, and with some of the acid, allowing some acid to pass through the tap. Then pour the acid you are going to use into the burette. The burette has markings on it to enable you to measure volumes accurately.

26
Q

What is the fourth step when carrying it a titration?

A

Record the reading on the burette. Then open the tap to release a small amount of acid into the flask. Swirl the flask to make sure that the two solution are mixed.

27
Q

What is the fifth step when carrying it a titration?

A

Keep repeating step four until the indicator in the flask changes colour. This shows when the alkali in the flask has completely reacted with the acid added in the burette. Record the reading on the burette and work out the volume of acid that has run into the flask. This volume is known as a TITRE.

28
Q

What is the sixth step when carrying it a titration?

A

Repeat the whole process at least three times. Discard any anomalous results. Alternatively, keep repeating the titration until you get two results within 0.1cm*3 of each other. Then calculate the mean to give you the most accurate result possible.

29
Q

What is the seventh step when carrying it a titration?

A

Use your results to calculate the concentration of the alkali in mol/dm*3.

30
Q

What solution goes into the burette?

A

The solution that you know the concentration of.

31
Q

What solution goes into the pipette?

A

The solution that you don’t know the concentration of. This ensures that you’ll know the volume of this solution accurately.

32
Q

What is the relationship between moles of gas and volume?

A

Equal numbers of moles of any gas occupy the same volume.

The volume of one mole of any gas is 24 dm*3 at room temperature and pressure at 20 degrees Celsius and 1 atmosphere.

33
Q

What is the equation for the number of moles of gas?

A

Number of moles of gas = volume of gas (dm3) / 24 dm3

Number of moles of gas = volume of gas (cm3) / 24000 cm3.

34
Q

What is the stoichiometry of the reaction?

A

The ratio of the number of moles of each reactant and product.

35
Q

What is the yield of a reaction?

A

The mass of the product that a chemical produces is called its yield.

36
Q

What is the percentage yield?

A

This compares the mass of product that the reaction actually produces with the maximum theoretical mass that it could possibly produce, as predicted from the balanced symbol equation.
The maximum mass possible is known as the theoretical yield of a reaction.

37
Q

What is the formula for percentage yield?

A

Percentage yield = actual mass of product produced / maximum theoretical mass of product possible.
X 100

38
Q

What factors affect percentage yield?

A

The reaction may be reversible.
Some reactants may react to give unexpected or unwanted products in alternative reactions.
Some of the products may be lost in handling or left in the apparatus.
The reactants may not be pure (as in the case if the lime kiln)
Some of the desired product may be lost during its separation from the reaction mixture.

39
Q

What is the atom economy?

A

The atom economy of a reaction is a measure of the extent to which the atoms in the starting materials (the reactants) end up in the desired product. Any remaining atoms end up in the other products.

40
Q

Hw do you calculate atom economy?

A

Percentage atom economy = relative formula mass of the desired product from equation / sum of the relative formula masses of the reactants from equation
X 100

41
Q

How do you calculate the concentration of a solution?

A

Concentration (g/dm3) = amount of solute (g) / volume of solution (dm*3).

Concentration (g/dm3) = amount of solute (g) / volume of solution (cm3) x 1000.

42
Q

Why might you carry out a titration?

A

To measure the exact volumes of acid and alkali needed to react with each other to form a neutral solution.

43
Q

What is the end point of a titration reaction?

A

The point at which the acid and alkali have reacted completely is called the end point of the reaction. You judge when the end point is reached by using an acid/base indicator.

44
Q

What is the first step when carrying it a titration?

A

Measure a known volume of alkali into a conical flask using a volumetric pipette. First wash the pipette with distilled water then with some of the alkali.

45
Q

What is the second step when carrying it a titration?

A

Add a few drops of acid/base indicator to the solution in the conical flask and swirl.

46
Q

What is the third step when carrying it a titration?

A

Rinse a burette with distilled water, and with some of the acid, allowing some acid to pass through the tap. Then pour the acid you are going to use into the burette. The burette has markings on it to enable you to measure volumes accurately.

47
Q

What is the fourth step when carrying it a titration?

A

Record the reading on the burette. Then open the tap to release a small amount of acid into the flask. Swirl the flask to make sure that the two solution are mixed.

48
Q

What is the fifth step when carrying it a titration?

A

Keep repeating step four until the indicator in the flask changes colour. This shows when the alkali in the flask has completely reacted with the acid added in the burette. Record the reading on the burette and work out the volume of acid that has run into the flask. This volume is known as a TITRE.

49
Q

What is the sixth step when carrying it a titration?

A

Repeat the whole process at least three times. Discard any anomalous results. Alternatively, keep repeating the titration until you get two results within 0.1cm*3 of each other. Then calculate the mean to give you the most accurate result possible.

50
Q

What is the seventh step when carrying it a titration?

A

Use your results to calculate the concentration of the alkali in mol/dm*3.

51
Q

What solution goes into the burette?

A

The solution that you know the concentration of.

52
Q

What solution goes into the pipette?

A

The solution that you don’t know the concentration of. This ensures that you’ll know the volume of this solution accurately.

53
Q

What is the relationship between moles of gas and volume?

A

Equal numbers of moles of any gas occupy the same volume.

The volume of one mole of any gas is 24 dm*3 at room temperature and pressure at 20 degrees Celsius and 1 atmosphere.

54
Q

What is the equation for the number of moles of gas?

A

Number of moles of gas = volume of gas (dm3) / 24 dm3

Number of moles of gas = volume of gas (cm3) / 24000 cm3.

Chemistry (38 decks)

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