Acids produce H+ in solution, example: HCl Bases produce OH- in solution, example NaOH
What is an acid? Acids are a group of chemicals. laboratory acids everyday acids Can you think of other examples of acids?
What is a weak acid? Strong acids cannot be touched and are corrosive. Weak acids are safe to handle and have a sour taste.
What is a strong acid? Some acids, like those found in the laboratory or a car battery, are very dangerous (too dangerous to taste or touch). These acids are said to be corrosive as they can damage other materials by wearing them away!They are strong acids. Why must strong acids always be handled very carefully?
What is a base? Bases are another group of chemicals, the opposite of acids. everyday bases laboratory bases Can you think of other examples of bases?
What is a weak base? Bases are used for cleaning. Strong bases are caustic and cause redness on the skin. Weak bases are soapy and safe to touch.
What is a strong base? Some bases, like those in the laboratory or in cleaning materials such as toilet cleaner, are too dangerous to touch. These bases are said to be caustic because they can burn skin and damage other materials! They are strong bases. Why must strong bases always be handled very carefully?
What is the pH scale? The strength of an acid or base is measured by the pH scale. Each universal indicatorcolour is given a number called the pH value. Universal indicator can tell you the pH of a solution. strongeracid stronger base 1 2 3 4 5 6 7 8 9 10 1112 1314 strongacid weak base weakacid strongbase neutral
Are these substances acidic or basic? Are they weak or strong? What type of substance? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 acid base very weak acid very strong acid very weak base weak base strong acid very strong base weak acid
What is an indicator? How can you test a liquid to find if it is an acid or an base? An indicator is a special chemical that changes to a different colour in an acid or an base. Litmus paper and litmus solution are examples of indicators. Litmus is red in acid. Litmus is blue in base.
Litmus paper cannot distinguish between a weak acid and a strong acid (or weak base and strong base). A better indicator is required…
What is universal indicator? Litmus is used to show if a solution is acid or base. Litmus does not show if the acid or base is weak or strong. Universal indicator has a range of colours that indicate the difference between weak or strong acids or bases. strongeracid stronger base strongacid weak base weakacid strongbase neutral
#1: Neutralization The GENERAL reaction betweenan acidandan base is calledneutralization. acid base a salt water What happens to the pH value of the reaction mixture during neutralization? The pH value of the reaction mixture becomes closer to 7.
#1: Neutralization The EXAMPLE for the chemical reaction between anan acidandan basecan be written as: H2O NaCl NaOH HCl
#1: Neutralization The GENERAL reaction between anan acidanda carbonate can be written as: acid carbonate H2O salt CO2
#1: Neutralization The EXAMPLE of a chemical reaction between anan acidanda carbonatecan be written as: 2HCl Na2CO3 2NaCl H2O CO2
#3: Metals with Acid General Reaction: HCl Mg MgCl2 H2 acid hydrogen salt metal Example:
Summary Chart All acids, bases and salts dissolve in water.
Summary of Reactions #1: Neutralization acid + base salt + water #2: Carbonate with acid acid + carbonate salt + water + carbon dioxide #3: Metal with acid acid + metal salt + hydrogen
Neutralizing stings A beesting isacidic. A wasp sting isalkaline. Why can bicarbonate of soda (pH 9) be used to treat a bee sting? Why can vinegar (pH 3) be used to treat a wasp sting?
Neutralizing soil Soils in different places can be acidic, alkaline or neutral. Many plants do not grow well in acidic soil. Why do farmers test soil to check the pH? Farmers often add an alkali to acidic soil to make their plants grow better. How does the alkali help to treat the acidic soil?
Neutralizing acid rain Gases emitted by cars, power stations and factories mix with rainwater in the atmosphere. This rainwater has a pH <5.5. Why is it called acid rain? Acid rain can have a harmful effect on the environment killing trees, polluting lakes and damaging buildings. How can the effects of acid rain be prevented?
Glossary • acid –A chemical that has a pH less than 7. • base –A chemical that has a pH greater than 7 and dissolves in water. • indicator –A special chemical that changes into different colours in acid and base solutions. • neutral –A chemical with a pH of 7 that is not an acid or a base. • neutralization –The chemical reaction between an acid and a base. • pH scale – The range of values that shows how strong or weak an acid or base is. • universal indicator – The indicator that shows the pH value of a chemical.