Elements the Periodic Table and the hidden structure of atoms.
How to succeed in Chemistry
Work in short bursts. You should be able to go through the content of this post in about 20 minutes. Don’t rush, there is some thinking involved. Don’t move onto the next stage until you are confident with this material. Take the test in a separate post when you are ready
Introduction for numpties
No matter how difficult Chemistry may seem the whole subject is based on simple ideas. Chemists only work with three types of particle, atoms molecules and ions. Once you understand the forces that hold these particles together and how they react with each other you can call yourself a chemist. We will start with atoms and ions and deal with molecules later. How do we identify atoms
Elements
Elements are pure substances that are made up of only one type of atom. Each element has a unique identifying number known as its atomic number.
When the elements are listed in order of increasing atomic number in table form interesting patterns appear. Elements in vertical columns on the periodic table have similar properties. Work through the Prezi featuring elements in the first column and elements from the last two columns.
The Atomic number
The Atomic Number identifies an atom, If we see a number 7 on the back of a Manchester United shirt we know its Beckham and we know he can bend the ball in flight
If we see an atom with an atomic number of 7 attached we know it is nitrogen and it is a gas that makes up 78% of the air we breathe. Every atom in the squad of elements that make up the periodic table has its own atomic number.
For example the atomic number of a lithium atom is three.The atomic number of a Sodium atom is 11. The atomic number of Potassium atom is 19. These three elements are found in the first column of the periodic table. Elements are arranged in rows on the table with the atomic number increasing by 1 as you move across. There are 18 columns in the periodic table. Elements in the same column have similar physical and chemical properties. Open up the interactive periodic table and click on the red elements to view videos showing how the elements react. Elements in the same column have similar properties. You should be familiar enough with the table to try the test at the end of this post.
Do the test, enter your email address and get feedback on how well you have done.
Acids change the colour of indicators such as phenolphthalein, litmus and universal indicator.
Acids react with certain metals to form hydrogen gas (zinc, magnesium, aluminium ,iron and other reactive metals but not copper) and a salt
Acids react with carbonates and hydogen carbonates (old fashioned name bicarbonates)
Acids react with bases or alkalis to form a salt and water.
Acids release hydrogen ions when they are dissolved in water.
Properties of Bases and Alkalis
All metal oxides and hydroxides are bases. Metal oxides don’t dissolve in water. Sodium hydroxide, potassium hydroxide, calcium hydroxide and ammonium hydroxide dissolve in water. Bases like these that dissolve in water are called alkalis.
Most household cleaning products contain contain bases. Oven cleaners contain sodium hydroxide (sometimes called caustic soda). Sodium hydroxide reacts with fat and grease to break them down. Soap is made when sodium hydroxide reacts with fats or oils.
Sodlum hydroxide feels soapy to touch because it reacts with fat and oil in your skin
Toothpaste contains a weak base to neutralise the acid produced by mouth bacteria.
Antacid tablets contain carbonates to react with and neutralise excess acid in the stomach.
Weak bases have a bitter taste and feel slippery to touch.
Bases change the colour of indicators (litmus phenolphthalein and universal indicator)
Bases react with acids to form a salt and water
Soluble bases (Alkalis) release hydroxide ions in solution)
Homework
Watch the video about using universal indicator to test the pH of different solutions. Watch also how the pH changes during a neutralisation reaction.
Answer the questions after it. To be handed in on Tuesday…..have a good weekend.
why should you wear gloves when using Mr Muscle?
What pH would you predict for toothpaste? What colour would universal indicator turn when it is used to test the pH of toothpaste?
What colour is phenolphtalein in acid solution?
What colour is phenolphthalein in basic solution
What colour does universal indicator turn when it is added to vinegar? What is the pH of vinegar?
What colour does universal indicator turn when it is added to Mr Muscle. What is the pH of Mr Muscle?
What colour does universal indicator turn when it is added to baking soda (sodium hydrogen carbonate) in solution. What is the pH of baking soda solution?
What colour does universal indicator turn when it is added to lemon juice. What is the pH of lemon juice?
What colour does universal indicator turn when it is added to a solution of table salt. What is the pH of salt solution? Why does salt solution have this pH?
What is the PH of sodium hydroxide solution. Is it a strong or weak base?
What is the pH of hydrochloric acid solution? Is it a strong or weak acid?
When vinegar is neutralised with sodium hydroxide the hydrogen ions are removed and the pH of the solution changes till it reaches a pH of 7 (completely neutral) Describe the colour changes you would see when vinegar is neutralised with sodium hydroxide solution. (Use the colours from the colour chart.
Writing fully balanced chemically equations.
………but first a reminder about salts and word equations
When hydrochloric acid reacts with a base and is neutralised salts known as chlorides are produced.
When sulphuric acid reacts with a base and is neutralised salys known as sulphates are produced.
When nitric acid reacts with a base and is neutralised salts known as nitrates are produced.
Here are the general word equations for reactions you need to know about.
acid + base —-> salt + water (bases are metal oxides and hydroxides)
acid + carbonate —–> salt + carbon dioxide + water
acid + hydrogen carbonate —–> salt + carbon dioxide + water
acid + metal —-> salt + hydrogen
Now complete each word equation, write down the chemical formulae and finish with a fully balanced chemical equation.
copper oxide + nitric acid —->
sodium hydroxide + sulphuric acid —->
calcium carbonate + hydrochloric acid —->
magnesium + hydrochloric acid
hydrochloric + sodium hydrogen carbonate —->
Use the table of ions from your text book to help write chemical formulae
Thiosulphate (doesn’t matter what the formula is but thio as a prefix indicates a sulphur compound) ions react with the hydrogen ions in acids to produce a thick precipitate of sulphur. The reaction happens faster at higher temperatures.
We can compare speeds of sprinters by measuring how long it takes for them to run a fixed distance, 100m. The world record held by Usain Bolt is quoted as a time, 9.58 seconds. The smaller the time taken to cover 100 meters the faster the speed.
We can time how quickly enough sulphur is produced by the thiosulphate ions to completely block a black band on the back of a test tube.The equation for this reaction can be written as:
Thiosulphate ions + hydrogen ions —–> sulphur + other products
Homework:
Watch the video. Decide how long it takes for each reaction in the video to produce enough sulphur to hide the black mark.Draw up a table of results. Plot a graph of temperature against time taken for the reaction( temperature goes on the horizontal axis, this is the variable you have control over.
Do an experimental write under the headings (on loose paper)
Aim
equipment
Diagram
Method
table of results
graph
Conclusion. What happens to the rate of reaction as the temperature increases?
Discussion: Use particle theory to explain the effect of heat on the rate of reaction with thiosulphate and hydrogen ions. Words to use in the discussion include activation energy, kinetic energy, effective collisions, frequency of collisions.
Play the presentation Chemical equations and calculations. Pay particular attention to the worked example before doing the example at the end of this post
Example to be handed in tomorrow
Hydrochloric acid solution was titrated with standard sodium hydroxide solution.
Before the titration the acid was diluted by making 1ml of solution up to 20ml(1:20) in a volumetric flask
20 ml samples of the acid in conical flasks were titrated by running standard sodium hydroxide solution ( 0.15 molL-1 concentration) in from a burette using phenolphthalein indicator
Titration Results
Volume of hydrochloric acid=20ml
Titration
rough
titration 1
titration 2
titration 4
titration 5
Final volume (ml)
26.35
49.60
24.50
50.00
47.80
Initial volume (ml)
00.00
25.20
00.20
27.00
23.30
Titre (ml)
26.35
24.40
24.30
23.00
23.50
On your own paper:
write the heading Titration Calculation
Copy the table of results beneath
select three concordant results and calculate the average titre
Write down the balanced chemical equation for the reaction
Use the method you have been shown to calculate the concentration of the hydrochloric acid