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Form 3 Chemistry Questions and Answers on The Mole

Chemistry form 3 questions and video answers on the mole.
Many questions from previous KCSE exams on the mole will be tackled in this course.

Lessons (34)

• 1.    5 g of calcium carbonate was strongly heated to a constant mass. Calculate the mass of the solid residue formed (Ca =40.0, C = 12.0 and O= 16.0)
  5m 7s

• 2.    A solution contains 40.3 g of substance XOH per litre. #25.0 cm^3#of this solution require #30.0 cm^3# of 0.3M Sulphuric (IV) acid for complete neutralization. a).Calculate the number of moles of XOH that reacted. b).Determine the relative atomic mass of X. (KCSE 2019 paper 1 question 7.)
  8m 21s

• 3.    An experiment was carried out to prepare crystals of magnesium sulphate. Excess magnesium powder was added to #100cm^3# of dilute sulphuric (VI) acid in a beaker and warmed until no further reaction took place. The mixture was filtered and the filtrate evaporated to saturation, then left to cool for crystals to form. a).i).Write an equation for the reaction.
  16m 36s

• 4.    Distinguish between empirical and molecular formula of a compound. (KCSE 2018 paper 1 question 28.)
  5m 20s

• 5.    #(NH_4 )_2 HPO_4# is a fertilizer used by farmers to boost their crop production. a).Calculate the mass of phosphorous in a 20 kg packet of #(NH_4 )_2 HPO_4# (N =14.0;H = 1.0;P = 31.0;O = 16.0) b).State one advantage of the fertilizer, #( NH_4 )_2 HPO_4# ,over urea #CO(NH_2)_2# (KCSE 2018 paper 1 question 27.)
  4m 49s

• 6.    #30.0 cm^3# of aqueous sodium hydroxide containing 8.0g per litre of sodium hydroxide were completely neutralized by 0.294 g of dibasic acid. Determine the relative formula mass of the dibasic acid. (Na = 23.0; O= 16.0 ; H = 1.0).
  6m 41s

• 7.    When 0.048g of magnesium was reacted with excess dilute hydrochloric acid at room temperature and pressure, #50 cm^3# of hydrogen gas was collected. (Mg =24.0; Molar gas volume = #24.0dm^3# ) i).Draw a diagram of the apparatus used to carry out the experiment described above. ii).Write the equation for the reaction. iii).Calculate the volume of the hydrogen gas collected.
  11m 49s

• 8.    #20 cm^3# of ethanoic acid was diluted to #400cm^3# of solution. Calculate the concentration of the solution in moles per litre (C = 12.0;H=1.0;O= 16.0 and the density of ethanoic acid is #1.05 g per cm^3# (KCSE 2017 paper 1 question 10.)
  4m 13s

• 9.    The empirical formula of lead (II) oxide was determined by passing excess dry hydrogen gas over 6.69 g of heated lead (II) oxide. a).What was the purpose of using excess dry hydrogen gas? b).The mass of the lead was found to be 6.21 g. Determine the empirical formula of the oxide. (Pb = 207.0 ; O = 16.0). (KCSE 2017 paper 1 question 4)
  4m 42s

• 10.    When 8.53 g of sodium nitrate were heated in an open test tube, the mass of oxygen gas produced was 0.83g. Given the equation of the reaction as #2NaNO_3(s) rightarrow 2NaNO_2 (s) + O_2(g)# Calculate the percentage of sodium nitrate that was converted to sodium nitrite. (Na =23.0 ;N =14.0 ;O = 16.0) (KCSE 2016 paper 1 question 7)
  4m 57s

• 11.    Calculate the mass of zinc oxide that will just neutralize dilute nitric(v) acid containing 12.6 g of nitric (v) acid in water ( Zn = 65.0 ;O =16.0 ;H =1.0 ; N=14.0 ) (KCSE 2015 paper 1 question 5).
  3m 39s

• 12.    A hydrocarbon contains 14.5% of hydrogen .If the molar mass of the hydrocarbon is 56, determine the molecular formula of the hydrocarbon. (C=12.0; H=1.0) (KCSE 2015 paper 1 question 26.)
  3m 21s

• 13.    An organic compound had the following composition 37.21% carbon, 7.75% hydrogen and the rest is chlorine. Determine the molecular formula of the compound given that the molecular mass of the compound is 65. (C=12.0 ; H =1.0 ;Cl =35.5). (KCSE 2014 paper 1 question 25).
  6m 3s

• 14.    #100 cm^3# of 0.05M sulphuric (VI) acid were placed in a flask and a small quantity of anhydrous sodium carbonate added. The mixture was boiled to expel all the carbon (IV) oxide. #25cm^3# of the resulting solution required #18 cm^3# of 0.1 M sodium hydroxide solution to neutralize it. Calculate the mass of sodium carbonate added. (Na =23.0; O = 16.0 ;C= 12.0) (KCSE 2014 paper 1 question 13.)
  9m 5s

• 15.    A solution was made by dissolving 8.2 g of calcium nitrate to give 2 litres of solution. Determine the concentration of nitrate ions in moles per litre. (Ca = 40.0;N = 14.0; 16.0) (KCSE 2013 paper 1 question 24.).
  3m 51s

• 16.    When #15cm^3# of a gaseous hydrocarbon P, was burnt in #100cm^3# of oxygen, gaseous mixture occupied #70 cm^3# at room temperature and pressure. When the mixture was passed through potassium hydroxide, its volume decreased to #25 cm^3#. a).What volume of the oxygen was used during the reaction? b).Determine the molecular formula of the hydrocarbon. (KCSE 2013 paper 1 question 23)
  4m 39s

• 17.    #10cm^3# of concentrated sulphuric (VI) acid was diluted to #100cm^3#. #10cm^3# of the resulting solution was neutralized by #36cm^3# of 0.1M sodium hydroxide solution .Determine the mass of sulphuric (VI) acid that was in the concentrated acid. (S = 32.0; H = 1.0; O = 16.0) (KCSE 2012 paper 1 question 8)
  5m 54s

• 18.    50 Kg of ammonium sulphate #(NH_4 )_2 SO_4# and 30 Kg of urea #CO(NH_2 )_2# fertilizers were applied in two equal sizes of plots A and B to enrich their nitrogen content. Show by working which plot was more enriched with nitrogen. (N =14; S =32; O =16 ; C =12 ; H = 1) (KCSE 2011 paper question 19.)
  0m 0s

• 19.    When lead (II) nitrate is heated, one of the products is a brown gas. a).Write the equation of the reaction that occurs. b).If #0.290 dm^3# of the brown gas was produced; calculate the mass of the lead (II) nitrate that was heated. (R.F.M lead (II) nitrate =331; Molar gas volume = #24dm^3# ). (KCSE 2011 paper 1 question 7).
  5m 19s

• 20.    Analysis of a compound showed that it had the following composition; 69.42% carbon,4.13% hydrogen and the rest oxygen. a).Determine the empirical of the compound (C=12.0 ;H =1.0; O=16.0) b).If the mass of one mole of the compound is 242, determine its molecular formula. (KCSE 2010 paper 1 question 17.)
  6m 12s

• 21.    Zinc metal and hydrochloric acid reacts according to the following equation. #Zn(s)+2HCl(aq) ZnCl_2(aq) +H_2(g)# 1.96g of Zinc metal were reacted with #100cm^(3)# of 0.2M hydrochloric acid. (a) Determine the reagent that was in excess. (b) Calculate the total volume of hydrogen gas that was liberated at S.T.P.[Zn=65.4,molar gas volume =22.4 litres at S.T.P]
  4m 56s

• 22.    A compound has an empirical formula, #C_3H_6O# and a relative formula mass of 116. (a) Determine its molecular formula. (H=1.0, C=12.0, O=16.0) (b) Calculate the percentage composition of carbon by mass in the compound.
  3m 42s

• 23.    0.63g of lead powder were dissolved in excess nitric (v) acid to form lead nitrate solution. All the lead nitrate solutionwas reacted with sodium sulphate solution. (a) Write ionic equation for the reaction between lead nitrate and sodium sulphate solutions. (b) Determine the mass of the lead salt formed in (a) above. (Pb =207.0, S=32.0,O=16.0)
  2m 52s

• 24.    On complete combustion of a sample of hydrocarbon, 3.52 g of carbon (IV) oxide and 1.44g of water was formed. Determine the molecular formuls of the hydrocarbon. (Relative molecular masses of hydrocarbon =56, carbon(IV) oxide=44, water=18 and relative atomic masses H=1.0 and C =12.0)
  4m 38s

• 25.    4.76g of liquid ammonia and 4.76g of liquid nitrogen were each allowed to warm up and change into gas at room temperature and pressure. Relative atomic masses:H=1.0 and N=14.0. Using the data given above, explain which gas occupied the greater volume.
  2m 28s

• 26.    #20.0cm^(3)# of asolution containing 4g per litre of sodium hydrioxide was neutralized by #8.0cm^(3)# of dilute sulphuric (VI) acid. Calculate the concentration of sulphuric (VI) acid in moles per litre. (Na =23.0,O=16.0, H=1.0)
  4m 34s

• 27.    A weighed sample of crystalline sodium carbonate #(Na_2CO_3.nH_2O)# was heated in a crucible until there was no further change in mass. The mass of the sample reduced by 14.5%. Calculate the number of moles(n) of the water of crystallization. (Na =23, O=16,C=12,H=1)
  3m 59s

• 28.    In an experiment, #30cm^(3)# of 0.1 M sulphuric acid were reacted with #30cm^(3)# of 0.1 M sodium hydroxide (a) Write an equation of the reaction that took place. (b) State the observation that were made when both blue and red litmus papers were dropped into the mixture. (c) Give a reason for your answer in (b) above.
  3m 49s

• 29.    When excess lead nitrate solution was added to a solution containing sodium chloride, the precipitate formed was found to weigh 5.56g. Determine the amount of sodium chloride in the solution. (Pb=207,C=35.5 Na =23).
  5m 14s

• 30.    When excess dilute hydrochloric acid was added to sodium sulphite, #960cm^(3)# of sulphur (IV) oxide gas was produced. Calculate the mass of sodium sulphite that was used. (molar mass of sodium sulphite=126g and molar gas volume =#24000cm^(3)#
  3m 58s

• 31.    The set up below was used to prepare hydrogen gas (a) Complete the diagram to show how dry sample of hydrogen gas can be collected. (b) Write an equation for the reaction which takes place when hydrogen gas burns in air. (c) (i) 1.2 litres of hydrogen gas produced at room temperature and pressure when 3.27g of zinc was used. De
  5m 50s

• 32.    When #Xcm^(3)# of a solution of 0.5M magnesium nitrate were reacted with ammonium carbonate solution, the mass of magnesium carbonate formed was 8.4g. (a) Write the ionic equation for the reaction that took place. (b) Calculate the value of X. (C=12.0,Mg=24.0;O=16. 0)
  4m 5s

• 33.    When hydrocarbon was completely burnt in oxygen, 4.2g of carbon (IV) oxide and 1.71g of water were formed. Determine the empirical formula of the hydrocarbon (H=10;c=12.0;)=16.0)
  4m 28s

• 34.    When 94.5g of hydrated barium hydroxide, Ba(OH)2.nH2O were heated at constant mass,51.3g of anhydrous barium hydroxide were obtained. Determine the empirical formula of the hydrated barium hydroxide. (Ba=137.0;O=16.0;H=1.0)
  3m 56s