Acids and bases AS 90944

Properties of acids

  • Weak acids have a sour taste
  • 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.

  1. why should you wear gloves when using Mr Muscle?
  2. What pH would you predict for toothpaste? What colour would universal indicator turn when it is used to test the pH of toothpaste?
  3. What colour is phenolphtalein in acid solution?
  4. What colour is phenolphthalein in basic solution
  5. What colour does universal indicator turn when it is added to vinegar? What is the pH of vinegar?
  6. What colour does universal indicator turn when it is added to Mr Muscle. What is the pH of Mr Muscle?
  7. 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?
  8. What colour does universal indicator turn when it is added to lemon juice. What is the pH of lemon juice?
  9. 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?
  10. What is the PH of sodium hydroxide solution. Is it a strong or weak base?
  11. What is the pH of hydrochloric acid solution? Is it a strong or weak acid?
  12. 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.
  13. 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

 

 

Earth Science test final preparation

Have a look through the course notes. They are divided into important sections.

Evidence for plate tectonics (slides 2-17)

Structure of the earth (slides 20-23)

Convection spreading and subduction (slides 24-26)

Taupo volcanic zone (slides 27-50) The main slides to consider here are: 28 animated view of australian plate melting,29 description in words, 30 and 31 Andesite  and rhyollite volcanoes (composite and caldera cones).

The Rock Cycle (slides 51-65). The main slide to consider here is 51. You must however be able to describe fully the processes involved in producing igneous sedimentary and metamorphic rocks.

Earthquake activity in the South Island. (slides 67-70 need to be studied carefully).

Marble: a metamorphic rock slides 71 and 72

How is an earthquakes origin determined. Earthquake sensing stations

Model answer for question 9 on the Rock Cycle in the previous post

Molten Magma is formed when rocks melt at high temperatures deep in the Earth’s crust or upper mantle. When this magma cools and crystallises it becomes Igneous rock, When the magma cools and solidifies on the surface it is known as volcanic igneous rock. When magma cools and solidifies before it reaches the surface it is known as intrusive igneous rock. Rocks which are exposed on the surface are eventually broken down by weathering and erosion and can be carried away rivers and glaciers, They are deposited as sediments when rivers enter the sea. As layers of sediment build build up to a depth of many kilometers compaction and cementation produces sedimentary rocks. These rocks are eventually changed due to pressure and heat, creating what is called Metamorphic rock.Metamorphic rocks never become molten. When this Metamorphic rock is exposed to excessive heat, it is melted and becomes magma and the cycle restarts.

Earth Science test preparation

Use the notes to answer the questions in the test preparation quiz. Please make sure you have completed this by 8pm on Sunday. It is not set up to autograde so you will need to wait for results.The long answer questions need to be marked individually. NOTE The presentation may take a short time to load fully

Take time to tackle this carefully and give full answers. Good luck.

 

The Periodic Table of Elements an Introduction

sodium and chlorine react

Work through The Introduction to the Periodic Table Prezi then check your understanding using the auto graded test. This is primarily intended for Rotorua Boys High year 11 students but anyone can use it. Let me know if you have any problems

By the end of this unit you should know:

  • what the atomic number and mass number of an element is.

  • how elements are arranged on the periodic table.

  • what Periods and Groups are.

  • the physical and chemical properties of the group 1 metals.

  • the physical properties of group 17 elements.

  • the physical properties of group 18 elements

  • that sodium and chlorine react violently together.

  • that elements in the same group have similar properties. WHY!

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