2.2 - Acid, bases and salts Flashcards
What are Indicators?
Substances that change colour when they are added to acidic or alkaline solutions
What is an acidic solution?
A solution with a pH less than 7
The lower the pH the stronger the acid
What is an alkaline solution?
A solution with a pH greater than 7
The higher the pH the stronger the alkali
An alkali is a base dissolved in water
What is the pH of a neutral solution?
pH 7
When Acids are dissolved in water what ions are produced?
Hydrogen ions, H+, sometimes called protons because hydrogen ions are the same as a hydrogen nucleus (which is a proton). Hydrochloric acid:
HCl(aq) → H+(aq) + Cl–(aq)
When Alkalis are dissolved in water what ions are produced?
Hydroxide ions, OH-
Sodium hydroxide:
NaOH(aq) → Na+(aq) + OH–(aq)
What is a base?
A base is chemically opposite to an acid. Some bases dissolve in water and are called alkalis. Other bases, including many metal oxides, do not dissolve in water
When the H+ ions from an acid react with the OH– ions from an alkali, a neutralisation reaction occurs to form water. What is the equation for this reaction?
H+(aq) + OH–(aq) → H2O(l)
What is a strong acid?
An acid which fully dissociates (separates or splits into smaller particles) to release H+ ions in an aqueous solution
What is a weak acid?
An acid that partially dissociates (separates or splits into smaller particles) to release H+ ions in an aqueous solution
In a reaction is the rate of reaction higher with a strong or weak acid?
Strong. The rate of reaction of strong acids with substances (such as metals, metal carbonates etc) is higher than that of weak acids.
What is a strong base?
A base which fully dissociates (separates or splits into smaller particles) to release OH- ions in an aqueous solution
What is a weak base?
A base that partially dissociates (separates or splits into smaller particles) to release H+ ions in an aqueous solution
What is a dilute acid?
A dilute acid has the acid molecules mixed with a large amount of water, so that there is only a low concentration of H+ ions.
What is a concentrated acid?
Concentrated acids have little to no water molecules mixed with the acid molecules, meaning the concentration of H+ ions is high.
In a reaction is the temperature rise greater with a weak or strong acid?
Strong. This means that the pH values of strong acids are lower than that of weak acids.
What is the product formed when a metal is added to a dilute acid?
Acid + metal → salt + hydrogen
Hydrochloric acid + zinc → zinc chloride + hydrogen
2HCl + Zn → ZnCl2 + H2
The hydrogen causes bubbling during the reaction. How can this be detected?
Using a burning splint which produces a squeaky pop sound
Generally the more reactive the metal in the reactivity series, the faster the reaction. How can this be indicated?
Indicated by more bubbles being given off per sec from metals with higher reactivity
Is the reaction with acids and metals exothermic or endothermic?
Exothermic
What is the product formed when acids react with metals hydroxides
Acid + metal hydroxide → salt + water.
Nitric acid + lithium hydroxide → lithium nitrate + water
HNO3 + LiOH → LiNO3 + H2O
Is the reaction of metal hydroxides with acids exothermic or endothermic?
Exothermic
What is the product formed when acids react with bases?
Acid + base → salt + water
Nitric acid + magnesium oxide → magnesium nitrate + water
2HNO3 + MgO → Mg(NO3)2 + H2O
What is the product formed when acids react with carbonates?
Acid + metal carbonate → salt + water + carbon dioxide
Sulfuric acid + iron(II) carbonate → iron(II) sulfate + water + carbon dioxide
H2SO4 + FeCO3 → FeSO4 + H2O + CO2
The carbon dioxide causes bubbling during the reaction, which is observed as fizzing. How can this be detected?
It can be detected by passing the gas through limewater, which will go cloudy.
Is the reaction of metal carbonates with acids exothermic or endothermic?
Endothermic
Try and remember this:
Reaction is metal carbonates with acids.
This type of reaction can be used to test unknown solutions to see if they are acidic. Simply add a solution of sodium carbonate to the solution and if carbon dioxide gas is given off, the solution is acidic.
What is neutralisation?
The reaction of hydrogen ions, H+, with hydroxide ions, OH-, to from water H20
How can you test for the presence of carbonate (CO3–) ions?
Carbonates react with dilute acids to form carbon acid.
If the solution bubbles then CO2 is being given off so the solution contains carbonate ions.
What is a salt?
A salt is any compound formed by the reaction of an acid and a base
The name of a salt has two parts. Where does the first and second part come from?
The first part comes from the metal, metal oxide or metal carbonate. The second part comes from the acid.
Nitric acid always produces salts that end in _____ and contain the ____ ion, NO3–
Hydrochloric acid always produces salts that end in _____ and contain the _____ ion, Cl–
Sulfuric acid always produces salts that end in ____ and contain the _____ ion, SO4^2–
nitrate
chloride
sulfate
How are crystals of soluble salts formed?
1) Measure a set volume of acid
2) Heat the acid gently
3) Add the chosen base in excess, the acid has been neutralised when excess solids sink to the bottom
4) Filter the excess base using filter paper and a funnel
5) Heat the Salt solution to evaporate the water
6) Leave the rest to evaporate slowly so crystals of the salt form.
What is the filtration process in respect to separating excess base and salt solution?
1) The mixture (excess base and salt solution) is poured into the filter funnel containing filter paper.
2) The salt solution will drip through and leave behind the insoluble solids that
3) The salt solution and the insoluble solids have now been separated
To obtain the pure salt from the solution, we need to remove some of the water. The method used is called evaporation. How can you evaporate the water?
1) Using a Bunsen burner
2) Placing solution near radiator/ window ledge - his will evaporate the water much more slowly and will result in larger crystals.
Describe the process of evaporation when obtaining a salt from a solution?
1) A solution is placed in an evaporating basin and heated with a Bunsen burner
2) After a while of heating the solution will become more concentrated as lots of the solution will have evaporated
3) Finally once all the solution has evaporated you will just be left with the crystalised solute
What is titration used for?
A method to prepare solutions of soluble salts
To determine the relative and actual concentrations of solutions in acids/ alkalis
To make an insoluble salt 2 _____ (soluble/insoluble) salts need to react together in a precipitation reaction
soluble
Silver nitrate and sodium chloride are both soluble. When their solutions are mixed together, soluble sodium nitrate and insoluble silver chloride are made:
What is the worded equation for this reaction?
silver nitrate + sodium chloride → sodium nitrate + silver chloride
AgNO3(aq) + NaCl(aq) → NaNO3(aq) + AgCl(s)
What is the test for Sulfate ions?
First add dilute hydrochloric acid, followed by Barium chloride solution
A white precipitate will form if sulfate ions are present in the solution
What are the chemical formulas of: Hydrochloric acid Sulphuric acid Nitric Acid Ammonia
Hydrochloric acid -HCl
Sulphuric acid - H2SO4
Nitric Acid - HNO3
Ammonia - NH3
What is the method of titration used for?
Used for finding a concentration of an unknown solution. E.g. the concentration of an acid or alkali
What is the equipment / materials needed for titration and why are they needed?
a pipette to accurately measure a certain volume of acid or alkali
a pipette filler to use the pipette safely
a conical flask to contain the liquid from the pipette
a burette to add small, measured volumes of one reactant to the other reactant in the conical flask
What is the method of titration?
1) Use the pipette and pipette filler to add 25 cm3 of alkali to a clean conical flask.
2) Add a few drops of indicator and put the conical flask on a white tile.
3) Fill the burette with acid and note the starting volume.
4) Slowly add the acid from the burette to the alkali in the conical flask, swirling to mix.
5) Stop adding the acid when the end-point is reached (the appropriate colour change in the indicator happens). Note the final volume reading
The same method works for adding an alkali to an acid – just swap around the liquids that go into the conical flask and burette.
What is the titre?
The difference between the reading at the start and the final reading gives the volume of acid (or alkali) added
How do you calculate the concentration of a solution?
Concentration = mol/volume
Units of concentration is mol/dm^3
How do you convert something in cm to dm^3
Divide a volume in cm^3 by 1,000 to convert it to a volume in dm3.
How can you calculate the concentration of an unknown solution?
(volume of known solution ÷ volume of unknown solution) × concentration of known solution
