C8- Acids And Alkalis Flashcards Preview

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Flashcards in C8- Acids And Alkalis Deck (24):

How are hazards of acids or alkalis shown

By international symbols - they indicate the precautions needed to be taken when handling them


How is the acidity or alkalinity of a solution measured

With a ph scale of 0 - 14 7 = neutral

Indicators can be used - that change colour

Universal indicator is made from a mixture of different indicators


Tell me about the indicator litmus

Blue in alkaline solution

Red is acid


Tell about methyl orange indicator

Yellow in alkali

Red in acid


Tell me about the indicator phenolphthalein

Pink in alkali

Colourless in acid


What happens when an atom loses electrons

Positive ion is formed


What are polyatomic ions

Former when small groups of atoms held by covalent bonds lose or gain electrons - eg OH


When happens to ions in acids

They produce an excess of hydrogen ions (H+) when they dissolve in water


What happens to ions in alkalis

Alkalis produce exceed hydroxide ions in water


How does concentration change

The higher the number of hydrogen ions in a certain volume, the higher a concentration

Same with alkalis with hydroxide ions

Neutral solutions - eg pure water have low and equal concentrations of hydrogen ions and hydroxide ions


What are bases

Substances that neutralise acids to form a salt and water only

All metal oxides are based


What happens in neutralisation

Hydrogen ions in the acid combine with oxide ions to form water

This removes hydrogen ions and so the ph increases to become neutral

The salts are produced by replacing the hydrogen ions with metal ions


Why is an excess of base always added

To make sure that all the acid is used up


How do you make sure the prepared salt is pure

The mixture is filtered to remove the residue (unreactive metal oxide) from the filtrate, leaving only the salt and water


How do crystallisation of the salt occur

Allowing the water to evaporate - leaving crystals


What's a base that can dissolve in water

A soluble base is called an alkali wooow

Ph values above 7


Tell me about group 1 hydroxides - alkali bases

Eg NaOH - balance out

But group 2 tend to be like Ca(OH)_2 as more hydroxide needed to produce a neutral complex


What happens to temperature when the neutralisation reaction

The mixture becomes warmer


What's a balanced equations

The number of atoms of each element must be the same on both sides


What happens if you try get some soluble salts from alkalis with the solution NOT being neutral

Otherwise you will contaminate the salt with an excess of one reactant


How can you obtain a neutral solution with only water and salt



What happens in a titration

Acid is added from a burette to a fixed volume of alkali in a conical flask

Use a measuring cylinder to measure out the alkali but a pipete is more accurate for repeatable measurements

A few drops of indicator are added to the alkali so you can follow the reaction

The end point is when the indicator changes colour

Methyl orange or phenolphthalein are used Becuase their obvious colour changes give you a sharp end point


What's a burette

A tall peice of glassware with 0.1cm^3 graduations


Tell me the steps to make a pure dry salt

Carry out a titration

Note the exact volume of acid neutralise the alkali

Use the burette to add the correct volume of acid without the indicator

Evaporate the water from the solution formed