Key Calculations quiz

1. In a chemical reaction, the overall molar enthalpy is -87 kJ/mol. Is this reaction exothermic or endothermic?

Endothermic

Depends on the reagents

Exothermic

Depends on the temperature of the surroundings

Question 1 of 17

2. What is meant by the term empirical formula?

A chemical formula that shows the actual numbers of the different types of atoms in a molecule

Baby food for emperors

A method of calculating the ratios of masses in an equation

A chemical formula that shows the simplest ratio of the numbers of atoms in a compound

Question 2 of 17

3. What is the meaning of the term Molar Volume?

The volume of 1 mole of gas at 100 ⁰C (24 cm³ or 24,000 dm³)

The volume of 1 mole of gas at r.t.p (24 cm³ or 24,000 dm³)

The volume of 1 mole of gas at 100 ⁰C (24 dm³ or 24,000 cm³)

The volume of 1 mole of gas at r.t.p (24 dm³ or 24,000 cm³)

Question 3 of 17

4. Calculate the relative formula mass(Mr) of ethanol (C₂H₅OH)

45

25

41

46

Question 4 of 17

5. 0.5 dm³ of copper sulfate solution has a concentration of 0.1 mol/dm³. What amount of copper sulfate does it contain?

5 mol

0.2 mol

0.05 mol

2 mol

Question 5 of 17

6. To determine the formula of a metal oxide by combustion, magnesium is heated in a crucible. Why is a lid lifted from time to time?

To allow oxygen in so the magnesium fully reacts

To stop the crucible heating up too much

To allow some magnesium oxide smoke to escape

To allow carbon dioxide to escape

Question 6 of 17

7. What are the units for amount in Chemistry?

g per 100g of solvent

Grams

Moles

mol/dm³

Question 7 of 17

8. A sample of carbon contained 98.90% carbon-12 and 1.10% carbon-13. Calculate the relative atomic mass of carbon

(12x13)/100 = 1.56

((13x98.90)+(12x1.10))/100 = 12.99

((12x98.90)+(13x1.10))/100 = 12.01

(12+13)/2 = 12.5

Question 8 of 17

9. What mass of calcium bromide will fully react with 71g of chlorine?

240 g

120 g

200g

480 g

Question 9 of 17

10. In the thermal decomposition of calcium carbonate, we might expect 50g of calcium carbonate to produce 28g of calcium oxide. If instead only 24g of calcium oxide is produced, what is the percentage yield?

0.56 %

85.7 %

56 %

0.857 %

Question 10 of 17

11. Complete the following expression: Mᵣ =

mass² / amount (in moles)

mass x amount (in moles)

mass / amount (in moles)

amount (in moles) /mass

Question 11 of 17

12. Work out the empirical formula of an oxide of chlorine contains 7.1 g of chlorine and 1.6 g of oxygen.

Cl₄O

Cl₄O₂

Cl₂O₂

Cl₂O

Question 12 of 17

13. A compound that contained 24.24% Carbon. 4.04% Hydrogen and 71.72% Chlorine and has a relative molecular mass of 99. Calculate the empirical formula and the molecular formula.

Empirical formula is C₂H₄Cl₂. Molecular formula is C₂H₄Cl₂

Empirical formula is CH₂Cl. Molecular formula is C₂H₄Cl₂

Empirical formula is CH₂Cl. Molecular formula is CH₂Cl

Empirical formula is C₂H₄Cl₂. Molecular formula is CH₂Cl

Question 13 of 17

14. A graph shows the solubility of sodium chloride in water at 50°C is 34g/100g. At that temperature, what mass of sodium chloride will dissolve in 50g water?

17g

0.17g

0.68g

68g

Question 14 of 17

15. Use Q=mcΔT and c=4.18J/°C/g. A spatula of sodium fluoride is put into a boiling tube with 25cm³ of water. The temperature drops from 22.0°C to 18.6°C. What is the total heat energy change?

1944 J

1944 kJ

355 kJ/mol

355 J

Question 15 of 17

16. Describe how to carry out an acid-alkali titration

1) Pipette 25cm³ of alkali into a conical flask. 2) Add indicator. 3) Fill a burette with acid, record the initial volume. 4) Whilst swirling the flask, add the acid dropwise until the indicator changes colour. 5) Record the volume and calculate the volume of acid which was added. 6) Repeat until three concordant results (within 0.2cm³ of each other). 7) Result is the average of all concordant results.

1) Pipette 25cm³ of alkali into a conical flask. 2) Add indicator. 3) Fill a burette with acid, record the initial volume. 4) Whilst swirling the flask, add the acid dropwise until the indicator changes colour. 5) Record the volume and calculate the volume of acid which was added. 6) Repeat until two concordant results (within 0.2cm³ of each other). 7) Result is the average of all concordant results.

1) Pipette 25cm³ of alkali into a conical flask. 2) Add indicator. 3) Fill a burette with acid, record the initial volume. 4) Whilst swirling the flask, add the acid dropwise until the indicator is just about to change colour. 5) Record the volume and calculate the volume of acid which was added. 6) Repeat until three concordant results (within 0.2cm³ of each other). 7) Result is the average of all concordant results.

1) Pipette 25cm³ of alkali into a conical flask. 2) Add indicator. 3) Fill a burette with acid, record the initial volume. 4) Whilst swirling the flask, add the acid dropwise until the indicator is just about to change colour. 5) Record the volume and calculate the volume of acid which was added. 6) Repeat until two concordant results (within 0.2cm³ of each other). 7) Result is the average of all concordant results.

Question 16 of 17

17. In a combustion calorimetry experiment, 0.78g of ethanol (C₂H₅OH) produced 12,540 J of heat energy. Calculate the molar enthalpy change.

-369 kJ/mol (Amount = 0.78/23 = 0.034 mol. Answer = 12540/1000/0.034 = 369 kJ/mol)

-213 kJ/mol (Amount = 46/0.78 = 59.0 mol. Answer = 12540/59.0 = 213 kJ/mol)

-738 kJ/mol (Amount = 0.78/46 = 0.017 mol. Answer = 12540/1000/0.017 = 738 kJ/mol)

-425 kJ/mol (Amount = 23/0.78 = 29.5 mol. Answer = 12540/29.5 = 425 kJ/mol)

Question 17 of 17

Key Calculations quiz

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