Acids Flashcards

Question

Are nitrates insoluble?

Answer 1

Yes except silver chloride

Answer 2

Yes except those of barium and calcium

Answer 3

No, except those of sodium, potassium and ammonium

Answer 4

1. Pick the right acid and insoluble base (most metal oxides, metal carbonates, and metal hydroxides are insoluble) E.G. to make copper nitrate, mix nitric acid and copper carbonate 2. Then add the metal oxide, carbonate, or hydroxide to the acid, the solid will dissolve in the acid as it reacts, you will know when all the acid has been neutralised because the excess solid will sink to the bottom of the flask and remain there 3. You can then filter out the excess base to get the salt solution. To get pure, solid crystals of the salt, evaporate off the water -CuCO3 (s) + 2HNO3 (aq) --\> Cu(NO3)2 (aq) + CO2 (g) + H2O (l)

Answer 5

1. You cannot use the method above if you want to neutralise an acid with an alkali. Alkalis are soluble bases so you cannot filter them out if you add to much, and you cannot tell when you have added too much 2. You have to add exactly the right amount of alkali to just neutralise the acid, you need to use an indicator to show when the reaction is finished. The best way of doing this is to do a titration +Measure out a set amount of acid into a conical flask using a pipette. Add a few drops of indicator. - Slowly add alkali to the acid, using a burette until you reach the end point - that's when the acids been exactly neutralised and the indicator. 3. Then repeat using exactly the same volumes of alkali and acid but without an indicator so the salt is not contaminated with indicator 4. The solution that remains when the reaction is complete contains only salt and water - slowly evaporate off some water then leave the solution to crystalise. Filter off the dry solid and dry it. What's left is a pure dry salt. - To make a soluble salt which is sodium, potassium or ammonium salt then you use a titration method when you react an acid with a solution of sodium or potassium hydroxide or carbonate (or use ammonia solution)

Answer 6

1. If the salt you want to make is insoluble, you can use a precipitation reaction 2. You just need to pick two solutions that contain the ions you need, one containing the correct positive ion and the other the correct negative ion E.G. to make barium sulphate (which is insoluble) you need a solution which contains barium ions and one which contains sulphate ions 3. So you can mix barium chloride (most chlorides are soluble) with sulphuric acid -BaCl2 (aq) + H2SO4 (aq) --\> BaSO4 (s) + 2HCL (aq) 4. The salt is obtained by FILTER the mixture to get the precipitate. WASH the salt with PURE/Distilled water to remove any traces of other solutions. Finally the salt is LEFT TO DRY 5. Dissolve in water, add together and mix, filter, wash with distilled water, leave to dry

Answer 7

- Concentrations - Titrations allow you to find out exactly how much acid is needed to neutralise a quantity of alkali (or vice versa)

Answer 8

1. Using a pipette and pipette filler, add known volume of alkali (usually about 25cm cubed) to a conical flask, along with two or three drops of indicator 2. Fill a burette with the acid. Make sure you do this below eye level, because you do not want to be looking up if some acid spills over 3. Using the burette, add the acid to the alkali a bit at a time, giving the conical flask a regular swirl . Go especially slowly when you think the end pint (colour change) is about to be reached 4. The indicator changes colour when all the alkali has been neutralised, e.g. phenolphthalein is pink in alkalis, but colourless in acids 5. Record the volume of acid used to neutralise the alkali 6. It is best to repeat this process a few times, making sure you get (pretty much) the same answer each time, this makes for more reliable results -The solution is transferred to an evaporating dish and heated to partially evaporate the water causing crystallisation or can be left to slowly evaporate, which tends to give bigger crystals

Answer 9

Stops you from getting a mouthful of alkali

Answer 10

Pipettes measure only one volume of solution, fill the pipette to about 3cm above the line, then drop the level down carefully to the line

Answer 11

Burettes measure different volumes and let you add the solution drop by drop

Answer 12

1. Place dilute HNO3 in a beaker 2. Warm the beaker gently on a tripod and gauze, do not boil the acid 3. Remove the beaker from the gauze and add lead (II) oxide one spatula at a time, stirring the acid until no more dissolves 4. Allow the solution to cool until room temperature 5. Filter off any excess lead (II) oxide and collect the filtrate in the boiling tube 6. Add dilute HCL to the filtrate 7. Filter the precipitate with 20cm cubed of distilled water to remove excess acid 8. Dry the lead (II) chloride between pieces of filter paper and leave in a warm place to dry

Answer 13

-Because then you would have two soluble products at the end which you could not separate easily (lead chloride and water so would not be able to separate) -Instead: lead oxide and nitric acid = lead nitrate (soluble) and water (soluble): but this is ok as you filter the solution and there is excess lead oxide so you are left with lead nitrate solution -Add dilute HCL to the lead nitrate solution (creates a mixture) -Then you filter this, and lead (II) chloride stays in filter whilst the rest goes through

Answer 14

- By reacting an acid with a metal or an insoluble base (e.g. metal oxide or an insoluble metal carbonate) 1. Add insoluble salt of copper oxide to (a measured volume of acid using a measuring cylinder) sulphuric acid and stir, the copper oxide is added in small proportions to the acid in the beaker with stirring 2. Warm gently on a bunsen burner (to speed up reaction), stir the reaction mixture and add more copper oxide using the spatula until it is in excess, until no more copper oxide dissolves (do not boil), all the acid is neutralised and there should be a little left over solid 3. The solution turns blue as the reaction occurs, showing that copper sulphate has been formed 4. Filter the solution once it has cooled to remove excess copper oxide, using a filter funnel and filter paper 5. Collect filtrate and put it in an evaporating dish/basin 6. Leave solutionn in warm place for a few days to allow the crystals to from

Answer 15

1. As excess H2SO4 would have been hard to remove from the solution and so contaminated the solution at the end 2. To make sure the reaction is completed and all the sulphuric acid is used up in the reaction

Answer 16

- The solution went from colourless to blue (blue solution formed) and the black colour of copper oxide disappeared - Initially the copper oxides appears to be dissolved but when copper oxide added in excess the black colour remained - Not all the water was evaporated by heating the bunsen briner because you would not have got the crystals

Answer 17

Mole concentration = _mass concentration_ mass of 1 mole