Key Calculations quiz

1. 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?

355 J

355 kJ/mol

1944 kJ

1944 J

Question 1 of 17

2. In a chemical reaction, 250 kJ/mol is taken to break all the bonds and 280 kJ/mol is released when new bonds are formed. What is the overall molar enthalpy of the reaction?

+530 kJ/mol

-30 kJ/mol

+30 kJ/mol

-530 kJ/mol

Question 2 of 17

3. What is meant by the term molecular formula?

A method of calculating the mass needed to make a certain yield in an equation

A method of calculating the ratios of masses in an equation

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

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

Question 3 of 17

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

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 cm³ or 24,000 dm³)

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

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

Question 4 of 17

5. 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?

56 %

0.56 %

0.857 %

85.7 %

Question 5 of 17

6. What mass of carbon dioxide is produced when 24g of carbon undergoes completely combustion?

88g

176 g

44 g

24 g

Question 6 of 17

7. What is the meaning of the word mole in Chemistry?

A mole is a small burrowing mammal

Moles are the units for amount of substance. 1 mole of a substance is its relative formula mass in grams (e.g. 1 mole of magnesium is 24 g)

Moles are the units for amount of substance. 1 mole of an element is its atomic number in grams (e.g. 1 mole of magnesium is 12 g)

Moles are the units for amount of substance. (1 mole is 10 g of a substance)

Question 7 of 17

8. 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 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 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 two concordant results (within 0.2cm³ of each other). 7) Result is the average of all concordant results.

Question 8 of 17

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

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

(12+13)/2 = 12.5

(12x13)/100 = 1.56

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

Question 9 of 17

10. A beaker of 1.5 mol/dm³ calcium chloride solution contains 0.3 mol of calcium chloride. What is the volume of the solution?

0.2 dm³

0.002 dm³

4.5 dm³

0.45 dm³

Question 10 of 17

11. 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 200g water?

17g

0.68g

0.34g

68g

Question 11 of 17

12. State the units of molar enthalpy change.

mol/⁰C

kJ/mol

J/⁰C/mol

kJ/⁰C

Question 12 of 17

13. What is the equation linking moles, Mᵣ and mass

moles = mass x Mᵣ

mass = moles / Mᵣ

Mᵣ = mass x moles

moles = mass / Mᵣ

Question 13 of 17

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

25

46

45

41

Question 14 of 17

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

Cl₂O₂

Cl₂O

Cl₄O₂

Cl₄O

Question 15 of 17

16. To determine the formula of a metal oxide by combustion, magnesium is heated in a crucible. Why is a lid used?

To stop the escape of magnesium

To stop the escape of magnesium oxide smoke

To stop carbon dioxide escaping

To keep the magnesium warm

Question 16 of 17

17. An oxide of nitrogen contains 26% nitrogen and 74% oxygen and has a relative molecular mass of 108. Find the empirical and molecular formulae for the oxide.

Empirical formula is N₄O₁₀. Molecular formula is N₂O₅

Empirical formula is NO₂.₅ Molecular formula is N₂O₅

Empirical formula is N₂O₅. Molecular formula is also N₂O₅

Empirical formula is N₂O₅. Molecular formula is N₄O₁₀

Question 17 of 17

Key Calculations quiz

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