Question 5.1:
To determine the empirical formula of the compound, we need to find the ratio of the elements present in the compound.
Given:
Carbon (C) = 40%
Hydrogen (H) = 6.7%
Oxygen (O) = 53.3%
Step 1: Convert the percentages to moles.
Carbon:
40 g C x (1 mol / 12.01 g) = 3.33 mol C
Hydrogen:
6.7 g H x (1 mol / 1.008 g) = 6.65 mol H
Oxygen:
53.3 g O x (1 mol / 16 g) = 3.33 mol O
Step 2: Divide by the smallest number of moles to find the simplest whole number ratio.
C: 3.33 mol / 3.33 mol = 1
H: 6.65 mol / 3.33 mol = 2
O: 3.33 mol / 3.33 mol = 1
Empirical formula: CH2O
Question 5.2:
From the balanced chemical equation, 3 moles of Ag produce 1 mole of N2O.
Given:
3 moles Ag produce 1 mole N2O
So, 1 mole Ag produces 1/3 moles N2O
Given: 180 g Ag
Molar mass of Ag = 107.87 g/mol
Number of moles of Ag = 180 g / 107.87 g/mol = 1.67 mol
Number of moles of N2O produced = 1.67 mol x (1/3) = 0.56 mol
Volume of N2O produced at STP = 10 dm3
Molar volume at STP = 22.4 dm3/mol
Number of moles of N2O at STP = 10 dm3 / 22.4 dm3/mol = 0.446 mol
Percentage purity = (Actual moles / Theoretical moles) x 100
Percentage purity = (0.56 mol / 0.446 mol) x 100 = 125.56%
Question 5.3.1:
Given:
Mass of magnesium (Mg) = 40 g
Volume of phosphoric acid (H3PO4) = 50 dm3
Molar mass of Mg = 24.31 g/mol
Molar mass of H3PO4 = 98 g/mol
Number of moles of Mg = 40 g / 24.31 g/mol = 1.65 mol
Number of moles of H3PO4 = 50 dm3 / 22.4 dm3/mol = 2.23 mol
Since the ratio of Mg to H3PO4 is 3:2, magnesium is the limiting reagent.
Question 5.3.2:
From the balanced chemical equation, 3 moles of Mg produce 3 moles of H2.
Number of moles of H2 produced = 1.65 mol Mg x (3 mol H2 / 3 mol Mg) = 1.65 mol
Mass of hydrogen gas produced = 1.65 mol x 2.016 g/mol = 3.33 g
Question 5.3.3:
Volume of liquid produced = 480 cm3 = 0.48 dm3
Concentration of Mg3(PO4)2 = (moles of Mg3(PO4)2 / volume of liquid produced)
Concentration = (1.65 mol / 0.48 dm3) = 3.44 mol/dm3
Therefore, the concentration of the magnesium phosphate solution is 3.44 mol/dm3.
QUESTION 5 (23 marks]
Question 5.1 [4 marks]
A 100 g sample contains 40% carbon, 6,7% hydrogen and 53,3% oxygen.
Determine the empirical formula of the compound.
Question 5.2 [6 marks]
A sample of impure silver with a mass of 180 g was dissolved in excess
concentrated nitric acid according to the following equation.
3Ag (s) + 4HNO,(aq) - 3AgNO, (s) + NO(9)+ 2H,0(1)
If 10 dm of nitrogen monoxide gas is produced under STP conditions, what is
the percentage purity of the silver sample?
Question 5.3
Magnesium reacts with phosphoric acid to produce magnesium phosphate and
hydrogen gas.
3Mg (s) + 2H,PO, () - Mg,(PO, )zlaq) + 3H,(g)
Question 5.3.1 (5 marks]
If 40 g magnesium reacts with 50 dm of phosphoric acid at STP, determine the
limiting reagent.
Question 5.3.2 (3 marks]
Calculate the mass of hydrogen gas produced.
Question 5.3.3 (5 marks]
Using your answer for Question 5.3.2, calculate the concentration of the
magnesium phosphate solution if the volume of the liquid produced is
measured to be 480 cm.
TOTAL: 23
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