AQA Acids and Gas collection
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| In a gas collection procedure, a student uses a 50cm3 measuring cylinder to collect gas with a maximum error of +/-0.5cm3. She collects 18.5cm3. What is the percentage error? | %error = maximum error / measurement * 100= 0.5/18.5*100= 2.7%
Note: it is the measurement (18.5cm3) that you use; not the maximum volume(25cm3)!
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| How do you work out the %error, given the measurement and the maximum error? | %error= maximum error / measurement * 100
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| When you collect Carbon Dioxide bubbling through water into a measuring cylinder, the volume is less than expected. Why? | Some of the Carbon Dioxide dissolves in water
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| When you add acid through a tap funnel, the volume expected is more than expected. Why? | The acid takes space in the volumetric flask
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| When you collect a gas over water, what must you not forget? | To fill the measuring cylinder thatt will collect the gas!
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| What is the formula of Nitric Acid? | HNO3
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| What is the formula of Ethanoic Acid? | CH3COOH
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| What is the formula of Sulfuric Acid? | H2SO4
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| What is the formula of Sodium Hydroxide? | Na(OH)
Do you remember the charge on the Hydroxide ion?
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| What is the formula of Magnesium Carbonate? | Mg(CO3)
Do you remember the charge on the Carbonate ion?
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| What is the formula of Sodium Carbonate? | Na2(CO3)
Do you remember the charge on the Carbonate ion?
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| What is the formula of Magnesium Hydroxide? | Mg(OH)2
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| What is the "active chemical" in acids? | Hydrogen ion, H+
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| Define an acid. | A proton(H+) donor
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| Define a base | A proton (H+) acceptor
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| What is the formula of Ammonia? | NH3
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| What is the name and formula of the salt made from Nitric Acid and Sodium Hydroxide? | Sodium Nitrate. Easy: look at the first word.
Na(NO3). Do you remember the charge on the Nitrate ion?
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| What is the name and formula of the salt made from Sulfuric Acid and Sodium Hydroxide? | Sodium Sulfate. Easy: look at the first word.
Na2(SO4). Do you remember the charge on the Sulfate ion?
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| Define an Alkali. Give an example | A base that can dissolve in acid. For example all the Hydroxides
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| What is the formula of Potassium Hydroxide? | KOH
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| What is a weak base like Ammonia? | It is a base because it is only partially dissociated in water. NH3 + H2O <=> NH4+ + OH-
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| What is a strong base like Sodium Hydroxide? | It is a base that is fully dissociated in water. Na(OH)(s) + H2O --> Na+(aq) + OH-(aq)
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| Define amphoteric. Give an example. | A chemical that is able to both accept a proton and donate a proton. For example amino acids have a carboxylic acid group (-COOH) and an amino group (-NH2)
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| What is the name and formula of the salt made from Sulfuric Acid and Sodium Carbonate? | Sodium Sulfate. Easy: look at the first word.
Na2(SO4). Do you remember the charge on the Sulfate ion?
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| What is the equation for the reaction between Sulfuric Acid and Sodium Carbonate? | H2(SO4) + Na2(CO3) --> Na2(SO4) + H2O + CO2
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| What is the equation for the reaction between Sulfuric Acid and Sodium Hydroxide? | H2(SO4) + 2 Na(OH) --> Na2(SO4) + 2 H2O
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| What is the equation for the reaction between Nitric Acid and Calcium Hydroxide? | 2 H(NO3) + Ca(OH)2 --> Ca(NO3)2 + 2 H2O
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| What is the equation for the reaction between Phosphoric Acid and Sodium Carbonate? | 2 H3(PO4) + 3 Na2(CO3) --> 2 Na3(PO4) + 3 H2O + 3 CO2
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| What is the equation for the reaction between Phosphoric Acid and Ammonia? | H3(PO4) + 3 NH3 --> 2 (NH4)3(PO4)
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| What is the equation for the reaction between HydroChloric Acid and Ammonia? | HCl + NH3 --> (NH4)Cl
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| What is the percentage by mass of Nitrogen in (NH4)3(PO4)? | 28.2%
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| What is the percentage by mass of Nitrogen in (NH4)2(SO4)? | 21.2%
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| How do you work out the %by mass of an Element in a Compound? | 1)Count the number of atom of that Element in the compound;2)Multiply that number by the RAM;3) divide the mass of all the atoms of that element by the RMM x 100
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| What is an indicator? | A chemical that has a different colour in acidic solutions than in alkaline solutions
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| What is the end-point of a titration? | When the indicator changes colour
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| What chemical is placed in the burette? | A chemical of unknown concentration
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| What chemical is placed in the conical flask? | A chemical of known concentration
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| What is the outline of the procedure for a titration? | 1)Place unknown in a burette;2)Pipette 25cm3 of a known solution in a conical flask;3)add indicator in flask;4)place flask over white tile;5)open tap from burette;6)go dropwise near end point;7)record volume on burette;8)repeat until concordant results
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| How do you work out unknown concentration of acid, when 18cm3 of Unknown is needed to neutralise given 25cm3 of known concentration of alkali? | 1)Work out moles Alkali=conc x vol flask (25/1000;2)Work out moles Acid using stochio.ratio;3)Work out concentration Acid=moles/volume burette(18/1000)
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| What is the concentration of HydroChloric Acid when 22.75cm3 of acid neutralises 25cm3 of 0.125mol.dm-3 NaOH. Equation: HCl + Na(OH) --> NaCl + H2O | 0.137 mol.dm-3
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| What is the %uncertainty on a 250cm3 volumetric flask that measures +/- 0.8cm3 | 0.8/250*100=0.32%
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| What is the %uncertainty on a 50cm3 burette that measured a titre of 21.40 +/- 0.05cm3 | [(0.05)*2]/21.40=0.467%; the%error is taken on the TITRE, not on the total capacity of the burette; the titre is worked by DIFFERENCE so the error is doubled
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| What is the %uncertainty on a 2decimal places balance that measured a mass of 1.32g by difference | the uncertainty is half of the smallest division: 0.01/2=+/-0.005g
but there were two readings so double the error; the %uncertainty is 0.005x2/1.32*100=0.75%
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| The %uncertainty on a burette is more than 5%. How could you reduce that percentage? | Either reduce the numerator (ie take a more accurate burette; which is not very feasible) or increase the denominator (ie try to get a bigger titre by diluting the solution in the burette)
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