Key Calculations quiz

1. Name this piece of lab equipment

pipette

gas syringe

burette

measuring cylinder

Question 1 of 17

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

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

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

Question 2 of 17

3. 25 cm³ of sodium chloride solution has a concentration of 0.5 mol/dm³. What amount of sodium chloride does it contain?

0.0125 mol

0.05 mol

12.5 mol

1.25 mol

Question 3 of 17

4. 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 kJ/mol

1944 kJ

355 J

1944 J

Question 4 of 17

5. What is meant by the term molecular formula?

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

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

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

Question 5 of 17

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

176 g

44 g

88g

24 g

Question 6 of 17

7. 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 7 of 17

8. 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?

68g

0.34g

17g

0.68g

Question 8 of 17

9. What volume does 0.5 moles of ethene gas occupy (at rtp)

12 cm³

12 dm³

48 dm³

48 cm³

Question 9 of 17

10. A sample of bromine contained the two isotopes in the following proportions: bromine-79 = 50.7% and bromine-81 = 49.3%. Calculate the relative atomic mass of bromine

(81 + 79)/2 = 80

((79x50.7)+(81x49.3))/100 = 79.99

((81x50.7)+(79x49.3))/100 = 80.01

(81x79)/100 = 63.99

Question 10 of 17

11. Calculate the relative formula mass(Mr) of zinc phosphide (Zn₃P₂)

257

120

272

223

Question 11 of 17

12. Complete the following expression: Mᵣ =

mass x amount (in moles)

mass / amount (in moles)

mass² / amount (in moles)

amount (in moles) /mass

Question 12 of 17

13. State the expression for calculating % yield.

% yield = (actual amount of products/theoretical amount of products)

% yield = (theroretical amount of products/actual amount of products) x 100

% yield = (theroretical amount of products/actual amount of products)

% yield = (actual amount of products/theoretical amount of products) x 100

Question 13 of 17

14. 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 keep the magnesium warm

To stop the escape of magnesium oxide smoke

To stop carbon dioxide escaping

Question 14 of 17

15. State the steps for calculating empirical formula

1) mass/Aᵣ. 2) divide by the largest. 3) Give the ratio has a whole number. 4) State final empirial formula

1) mass/Aᵣ. 2) divide by the smallest. 3) Give the ratio has a whole number. 4) State final empirial formula

1) Aᵣ/mass. 2) divide by the largest. 3) Give the ratio has a whole number. 4) State final empirial formula

1) Aᵣ/mass. 2) divide by the smallest. 3) Give the ratio has a whole number. 4) State final empirial formula

Question 15 of 17

16. What are the units for amount in Chemistry?

g per 100g of solvent

mol/dm³

Moles

Grams

Question 16 of 17

17. 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 CH₂Cl. Molecular formula is CH₂Cl

Empirical formula is C₂H₄Cl₂. Molecular formula is CH₂Cl

Empirical formula is CH₂Cl. Molecular formula is C₂H₄Cl₂

Empirical formula is C₂H₄Cl₂. Molecular formula is C₂H₄Cl₂

Question 17 of 17

Key Calculations quiz

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