ACIDS AND BASES
when an acid reacts with a base , a neutralisation reaction occours
example of this is brushing teeth with toothpaste neutralises acids
alkalis are are a part of a larger class of compounds , called bases
bases are compounds that can neutralize acids.
alklis are those bases that are soluble in water such as they hydroxides of group 1 metals.
Reactions
all the alkali metals are very reactive , they have to be stored in oil ,
Alkalai metals also react vigourusly with non metaals such as chlorine gas.
the elements in group one of the periodic table are called the alkali metals , their melting/boiling point decreases as we go down the group.
all metals react with water to produce hydrogen and an alkaline solution containing the metal hydroxide.
they form +1 irons in reactions to make ionic compounds
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Acids have a pH of less than seven, bases have a pH of more than seven. When bases are dissolved in water they are known as alkalis.
Hydrogen ions make a solution acidic – acids are corrosive
Hydroxide ions make a solution alkaline.
Equal numbers of hydroxide and hydrogen ions create a neutral solution. ( water)
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Indicators
The pH scale is the measure of how many hydrogen ions are present in a solution. Lots of hydrogen ions means strong acid, few hydrogen ions mean weak acid/alkali. Universal indicator is a combination of dyes which can be dropped into a solution to find the pH. However the colour you see and how acidic/alkali you think it is depends on your perception of colour.
Using litmus paper; an acid will go red, an alkali will go blue.
Reacting a strong acid + strong alkali We can use any indicator
Reacting a strong acid and a weak alkali We use Methyl Orange
Reacting a weak acid and strong alkali We use Phenolphthalein
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When metals react with carbonates such as calcium carbonate they form a salt, water and carbon dioxide. The co2 can be detected by bubbling the gas produced through lime water and seeing if it turns cloudy.
When metals react with carbonates such as calcium carbonate they form a salt, water and carbon dioxide. The co2 can be detected by bubbling the gas produced through lime water and seeing if it turns cloudy.
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The more reactive the metal, the faster the reaction will happen – very reactive metals react explosively.
The speed of the reaction can be told by the rate a which the hydrogen bubbles are produced.
We can test to ensure it is definitely hydrogen present by the burning split test – if we hear a squeaky pop then hydrogen is present.
However this reaction does not take place for all metals as metals below hydrogen in the reactivity series (less reactive than hydrogen) will not be able to displace the hydrogen in the acid – if this is the case then no reaction will occur. (e.g. in copper)
Note: That if we use a weak acid there are going to be fewer hydrogen ions available to react with the metal and so the rate of reaction will be slower with a weak acid but faster with a stronger acid.