Solve the following problems showing all work and using proper form. Hint: Determine the chemical formula by criss-crossing valence values. 1. Determine the composition of a substance made from 39.10g of potassium and 19.00g of fluorine. (3 mark) moles = 39.1/39.1 = 1 ; 19.00/19.00 = 1 chemical formula= Kf 2. Determine the composition of a substance made from 24.31g of magnesium and 159.82g of bromine. (3) moles = 24.31 = 1 ; 159/79.9 = 2 chemical formula = MgBr2 3. Determine the composition of a substance made from 21.62g of boron and 42.03g of nitrogen. (3) moles = 21.62/10.8 = 2 ; 42.03/14 = 3 chemical formula = B2N3 4. A sample of a compound has a percent composition of 71.47% calcium and the rest oxygen. If the sample has a mass of 87g, then what is the mass of each element in the sample? (3) mass of calcium = 87 X 71.47/100 = 62.18g mass of oxygen = 87 x 28.53/100 = 24.82g
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Pam O.
Calculate the number of moles represented by each of the following: a 20g of magnesium oxide, MgO b 3.20g of iron(III) oxide, Fe2O3 c 2kg of copper(II) oxide, CuO d 50g of copper(II) sulfate crystals, CuSO4·5H2O e 1 tonne of iron, Fe (1 tonne is 1000000g) f 0.032g of sulfur dioxide, SO2 (Ar: H = 1, O = 16, S = 32, Mg = 24, Fe = 56, Cu = 63.5) 6 The following calculations use Ar: H = 1, O = 16, Na = 23, Cl = 35.5, Ca = 40, Cu = 63.5. a Calculate the mass of 4 mol of sodium chloride, NaCl. b Calculate how many moles is 37g of calcium hydroxide, Ca(OH)2. c Calculate how many moles is 1 kg (1000g) of calcium, Ca. d Calculate the mass of 0.125 mol of copper(II) oxide, CuO. e 0.1 mol of a substance has a mass of 4g. Calculate the mass of 1 mole. f 0.004 mol of a substance has a mass of 1 g. Calculate the relative formula mass of the compound. 7 Determine the empirical formulae of the compounds which contain: a 9.39g P, 0.61g H b 5.85g K, 2.10g N, 4.80g O c 3.22g Na, 4.48g S, 3.36g O d 22.0% C, 4.6% H, 73.4% Br (by mass) (Ar: H = 1, C = 12, N = 14, O = 16, Na = 23, S = 32, K = 39, Br = 80) 8 1.24g of phosphorus was burnt completely in oxygen to give 2.84g of phosphorus oxide. Find: a the empirical formula of the oxide b the molecular formula of the oxide given that 1 mole of the oxide has a mass of 284g. (Ar: O = 16, P = 31) 9 An organic compound contained C 66.7%, H 11.1%, O 22.2% by mass. Its relative formula mass was 72. Find: a the empirical formula of the compound b the molecular formula of the compound. (Ar: H = 1, C = 12, O = 16) 10 In an experiment to find the number of molecules of water of crystallisation in sodium sulfate crystals, Na2SO4·nH2O, 3.22g of sodium sulfate crystals were heated gently. When all the water of crystallisation had been driven off, 1.42g of anhydrous sodium sulfate was left. Find the value of n in the formula. (Ar: H = 1, O = 16, Na = 23, S = 32)
Adi S.
If the total tared mass of a tin oxide formed in an experiment weighs 0.703 grams and it contains 0.544 g of Sn (formula weight = 118.7 amu), calculate the amount of oxygen it contains. Determine the simplest formula (empirical formula) of the oxide. (Only tin and oxygen are present in the compound. The formula weight of oxygen = 16.0 amu.) A student working to determine the empirical formula of a compound formed by the reaction of Ag and Oxygen collected the following set of data: Mass of crucible = 19.801 g Mass of Ag = 0.975 g Final mass of crucible and product = 20.849 g Molar mass of Ag = 107.87 g Calculate the amount of Oxygen consumed. Calculate the empirical formula of the compound formed. Calculate the experimental % composition of elements in the formula. Calculate the theoretical % composition of elements in the formula. If some magnesium oxide were lost by spattering, would it appear that your oxide product contained more or less oxygen? Explain the reasoning for your answer. How many significant figures will you report in the following calculations? 6.0 + (5.99 - 4.98) * 5. Justify your answer with calculations.
Punit I.
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