U1, S2 Amount of substance Flashcards
1) In the ideal gas equation, what should the units of pressure be?
1) Pa (pascals)
2) What does Avogadro’s constant represent?
the number of particles in one mole of a substance: 6.02 x 1023
3) How many atoms are there in 0.500 moles of pure krypton?
3) 3.01 x 1023.
Number of atoms = moles x Avogadro’s constant
= 0.500 × (6.02 x 1023) 3.01 x 1023
4) How many moles of scandium fluoride are there in 20.4 g of ScF3? Mr of ScF3 = 102.0.
4) 0.200 moles. Number of moles of ScF3
= mass/Mr = 20.4/ 102.0 =0.200 moles (3 s.f.)
5) What mass of selenium dioxide (SeO₂) needs to be dissolved in water to give 40.0 cm³ of a solution with a concentration of 0.500moldm-³? Mr of SeO₂ = 111.0.
5) 2.22 g.
Volume of solution in dm³ = 40.0 ÷ 1000 = 0.0400 dm³
Number of moles = concentration x volume
= 0.500 x 0.0400 = 0.0200 moles
Mass of SeO₂ = moles x Mr = 0.0200 x 111.0 = 2.22 g
6) At 200 kPa, 2.00 moles of a gas occupy a volume of 40.0 dm³.
Calculate the temperature of the gas sample.
Gas constant, R = 8.31 J K-¹ mol-¹.
7) What volume of water, in cm³, does 12.75 g of sodium nitrate (NaNO3) need to be dissolved in
to give a solution with a concentration of 1.50 mol dm-³? Mr of NaNO3 = 85.0.
8) At 37 °C and 100 kPa, a sample of gas with an Mr of 34.0 occupies a volume of 760 cm³.
Calculate the mass of the gas sample. Gas constant, R = 8.31 J K-¹ mol-¹.
1) What should the state symbol be for the lead iodide precipitate (Pbl₂) in the following equation?
Pb(NO3)₂ + 2KI → Pbl₂ + 2KNO3
1) (s)- it’s a precipitate, which means it must be solid.
2) Which of the following equations is balanced correctly? A. MnO₂ + 2KOH + O₂ → K₂MnO, + 2H₂O
B. 2PbS+ 2Na₂CO3 + C → 2Pb + 2Na₂S + 3CO₂
2) B (lf, by chance, you had a wave of equation-balancing enthusiasm and felt keen enough to fix equation Ar the correctly balanced equation would be:
2MnO₂ + 4KOH + O₂ → 2K₂MnO4 + 2H₂O.)
3) What does an ionic equation show?
3) An ionic equation shows only the reacting particles for a reaction happening in solution, and the products that they form.
4) The Haber process is used to make ammonia (NH3) from nitrogen and hydrogen gas.
Give the balanced equation for this reaction.
4) N₂ + 3H₂ → 2NH3
5) Balance the following equation: BeO + C → Be₂C + CO
5) 2BeO + 3C → Be₂C + 2CO
6) Potassium chloride solution reacts with silver nitrate solution to form potassium nitrate in solution and a silver chloride precipitate. Give the balanced ionic equation for this reaction.
The equation for this reaction is: KCI + AgNO3 → KNO3 + AgCl
7) Calcium reacts with nitric acid (HNO3) to produce a solution of calcium nitrate, Ca(NO3)2, and hydrogen gas. The equation for this reaction is: Ca + 2HNO3 (aq) →Ca(NO3)2(aq) + H₂ (g) Give the ionic equation for this reaction.
1) The neutralisation reaction of magnesium hydroxide with hydrochloric acid produces water.
What is the state symbol of water in the equation for this reaction?
1) (l) - water is a liquid. Don’t go thinking water has the symbol (aq) that’s used for a solution in water, and water in water would just be silly.
2) Calculate the mass of potassium chloride (Mr = 74.6) produced when 0.250 moles of potassium chlorate, KCIO3, fully decomposes in the following reaction: 2KCIO3 → 2KCI + 30₂
2) 18.7 g. From the equation, 2 moles of KCIO3 produce 2 moles of KCI, so 0.250 moles of KCIO3 produce 0.250 moles of KCI. Mass of KCI produced
= moles x Mr
= 0.250 x 74.6
= 18.65 = 18.7 g (3 s.f.)
5) 6.94 g of lithium nitride (Li,N) is made from the reaction of lithium and nitrogen: Li + N₂ → Li3N
Balance the equation for this reaction, and calculate the mass of lithium that has reacted.
1) Why can’t universal indicator be used as an indicator for a titration?
1) E.g. the colour change is too gradual / there’s no clear end point.
2) What is the purpose of a rough titration?
2) It gives an idea of where the end point of the titration is, before any accurate titrations are carried out.
3) How many grams of sodium carbonate (Na₂CO3) are needed to make 200 cm³ of 1.50 mol dm³ sodium carbonate standard solution? Mr of Na2CO3 =
106. 0.
4) The results for a titration are shown in the table on the right.
State which result is anomalous, and explain your reasoning.
5) Suggest a possible reason for the anomalous result.
6) Calculate the mean titre of the results, ignoring the anomalous result.
4) Titration 2 is anomalous as it is significantly different to the others.
5) E.g. the solution in the burette wasn’t added dropwise around the end point, meaning the exact point at which the colour changed was missed / wasn’t recorded accurately.