g1 Solve the following stoichiometric questions using dimensional analysis. Roun

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g1

Solve the following stoichiometric questions using dimensional analysis. Round all molar masses to two decimal points Na_2Si0_3(s) + 8 HF_(ad) right arrow H_2SiF_6(aq) + 2 NaF_(aq) + 3 H_2O(l) How many moles of HF are needed to produce 0.350 moles of H20? (2) How many grams of NaF form when 0.900 mol of HF reacts with excess Na_2SiO_3? ((3) How many grams of Na_2SiO_3 can react with 5.625 grams of HF? (4) c The 9-kg cottar has a velocity of 7 m/s to the right when it 11 al A It then travels down along the smooth guide shown The spring has an unstretched length of 100 mm and B is located just before the end of the Curved portion of the rod (Figure 1) Determine the speed of the collar when it reaches point B. Express your answer to three significant figures and Include the appropriate units.

Explanation / Answer

a) 3 moles of H2O are produced when 8 moles of HF reacts

Thus, 0.35 moles of H2O are produced when 8*0.35/3 = 0.934 moles of HF reacts

b) when 8 moles of HF reacts , 2 moles of NaF is formed

Thus, when 0.9 moles of HF reacts, 2*0.9/8 = 0.225 moles of NaF is produced

Molar mass of NaF = 42 g/mole

Thus, mass of NaF produced = moles*molar mass = 0.225*42 = 9.45 g

c) molar mass of HF = 20 g/mole

Thus, moles of HF in 5.625 g of it = mass/molar mass = 0.28125

Thus, as per the balanced reaction , Na2SiO3 & HF reacts in the molar ratio of 1:8

Thus, moles of Na2SiO3 reacting with 0.28125 moles of HF = 0.28125/8 = 0.0352

molar mass of Na2SiO3 = 122.06

Thus, mass of Na2SiO3 reacting = moles*molar mass = 4.29 g

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