⭐️SC8 - Acids and Alkalis Flashcards
For litmus:
- what colour is it In alkaline solutions?
- what colour is it in acidic solutions?
Blue in alkaline and red in acid
For methyl orange:
- what colour is it In alkaline solutions?
- what colour is it in acidic solutions?
Yellow in alkaline and red in acid
For phenolphthalein,
- what colour is it In alkaline solutions
- what colour is it in acidic solutions
Pink and colourless
When are polyatomic ions formed?
When small groups of atoms held together by covenant bonds loose or gain electrons e.g. OH-
What does a concentration depend on?
The number of hydrogen ions for an acid or hydroxide ions for an alkaline in a certain volume, so the higher the concentration of H+ ions, the more acidic the solution and the higher the concentration of OH- ions the more alkaline the solution
How is the concentration of H+ ions linked to the pH?
As if concentration increased by a factor of 10, the pH decreases by 1
What makes an acid strong?
The molecules of the acid dissociate completely into ions when they dissolve in water and produce high concentrations of hydrogen ions, they also have a low pH value
What are bases?
Substances that neutralise acids to form salts and water only
What is the general word equation for neutralisation reactions?
Metal oxide + acid -> salt + water
What happens to ions in general during neutralisation reactions?
Hydrogen ions in the acid combine with oxide ions to form water. This removes the hydrogen ions causing the pH to increase
In terms of ions how are salts produced in neutralisation reactions?
By replacing hydrogen ions with metal ions
When are bases alkali? What are these?
When they are soluble bases like sodium hydroxide and other group 1 hydroxides and calcium hydroxide and other group 2 hydroxides
What bases are not alkali? What are these?
Insoluble ones like copper hydroxide and most other metal hydroxides
What happens during a neutralisation reactions?
The reaction mixture becomes warmer when alkali is added to the acid and pH increases giving products of salt and water but pH may go higher than 7 if enough alkali is added
What happens to ions In a neutralisation reaction
The hydrogen ions from the acid react with hydroxide ions from the alkali and water being a simple molecular covalently bonded substance with molecular bonds is formed. The ions from the acid and alkali stay in solution as ions of the dissolves salt
How can you make a pure dry salt?
- Carry out a titration
- this gives the exact volume of acid needed to neutralise an alkali
- use the Burnett to add the correct volume of acid without any indicator
- evaporate the water from the solution formed
In a titration why do you use a Burette and not a measuring cylinder?
Because you can add one drop of acid at a time providing more accurate and repeatable measurements
What indicators are used in titration and why?
Phenolphthalein and methyl orange as they give you a sharp end point due to the obvious colour change
Give the general word equation for when you react metal and acids
Metal + acid -> salt + water
How do you test for hydrogen?
Put a light splint in a hydrogen and air mixture and you’ll hear a squeaky pop
What are oxidation and reduction?
Oxidation is loss of electrons
Reduction is the gain of electrons
What’s the general word equation when an acid reacts with a metal carbonate?
Metal carbonate + acid -> salt + water + carbon dioxide
What do you see in a reaction between a metal carbonate and an acid?
You can see bubbles (of the carbon dioxide) and the solid metal carbonate disappears (providing there’s enough acid )
What is a precipitate reaction “
Where soluble substances in solution cause an insoluble precipitate to form
In general what substances are soluble and what are insoluble
- All common sodium, potassium and ammonium salts
- all nitrates
- most chlorides except silver and lead chloride
- most sulphates except Lead, barium and calcium sulphate
- only sodium, potassium and ammonium carbonates, all others are insoluble
- only sodium, potassium and ammonium hydroxides, all others are insoluble
How can you test for carbon dioxide?
Bubble the gas through limewater and will turn milky if lime water is present
How can ionic equations show the formation of precipitates?
The formula of the ions the react together to form the precipitate is on the left and the formula of the precipitate is on the right
How can you predict wether a precipitate will form?
By checking the solubility of the product as if both products are insoluble then no precipitate forms
Give a method to prepare a pure dry sample of insoluble salt from two soluble ones
- Wear eye protection
- Mix the two solutions in a beaker and then filter the mixture
- Mix the beaker with a little distilled water and then pour it through the funnel
- Pour a little distilled water over the precipitate in the funnel. This is so little salt can be wasted from being stuck on the sides
- Carefully remove filter paper containing the precipitate and dry it in a warm oven
