Chemistry C4 - Calculations

Question 1

1. How do you calculate relative formula mass, Mr of a compound

Answer 1

1. Add together the atomic masses of every atom in a compound.

Question 2

2. What is the law of conservation of mass?

Answer 2

2. Conservation of mass says that atoms cannot be destroyed or created during a chemical reaction.

Question 3

3. Why would a reaction that produces a gas seem to decrease in mass?

Answer 3

3. Gas is lost to the atmosphere.

Question 4

4. Why would a reaction where a gas reacts seem to increase in mass?

Answer 4

4. The mass of the gas is now included in the product.

Question 5

5. What is a mole?

Answer 5

5. An amount of substance containing an Avogadro’s number of particles (6.02 x 1026)

Question 6

6. How does a mole link to Mr?

Answer 6

6. A mole is a substances Mr expressed in grams.

Question 7

7. What is a limiting reactant?

Answer 7

7. The reactant that is completely used up in a reaction. It controls the amount of product formed

Question 8

8. Why aren’t all % yields 100%?

Answer 8

8. The reaction may not go to completion or product may be lost.

Question 9

9. What is the volume of 1 mole of gas at 20oC and 1 atm of pressure?

Answer 9

9. 24dm3

Question 10

1. Moles from masses in g.

Answer 10

1. n=m/Mr where n=moles, m=mass in g & Mr=relative formula mass

Question 11

2. Convert cm3 to dm3

Answer 11

2. dm3 = cm3 /1000

Question 12

3. Mass concentration (g/dm3)

Answer 12

3. = mass (g)/volume (dm3)

Question 13

4. Molar concentration (mol/dm3)

Answer 13

4. =moles (mol)/volume (dm3)

Question 14

5. % Yield

Answer 14

5. =(actual yield/theoretical yield) x 100

Question 15

6. Atom economy

Answer 15

6. =(Mr of desired product/Mr of all reactants) x 100

Question 16

7. Moles (from gas volumes)

Answer 16

7. =Volume of gas (dm3)/24