The Periodic Table
What is an element?
A substance made up of one type of atom.
In a chemical reaction, what is the difference between a reactant and a product?
Reactants are the substances present at the start of a reaction. Products are the substances formed at the end.
Name two signs that a chemical reaction has taken place.
A colour change, a gas being produced, a precipitate (solid) forming, or a change in energy/temperature.
What is one example of an acidic substance, and one example of an alkaline substance?
Acidic: tomatoes, black coffee, vinegar, orange juice, stomach acid, battery acid
Alkaline: sea water, baking soda, soapy water, bleach, drain cleaner
A gas produced during an investigation turns limewater cloudy or milky. What is the gas?
Carbon dioxide.
Name the two elements that are liquid at room temperature.
Bromine and Mercury
What is the difference between a compound and a mixture?
A compound forms when elements are chemically bonded together. A mixture contains substances together that are not chemically bonded and can often be separated by physical methods.
Name two ways to make a chemical reaction happen faster.
Increase the temperature, increase the concentration, decrease the particle size, or add a catalyst.
A substance has a pH of 3. Is it acidic, neutral or alkaline?
Acidic. Acids have a pH below 7.
A forensic scientist suspects that a sample contains hydrogen gas. What test could they perform, and what result would they expect?
Hold a lit splint at the mouth of the test tube. Hydrogen burns with a squeaky pop.
Sodium and potassium are both in Group 1. What does this tell us about their chemical properties?
Elements in the same group have similar chemical properties and react in similar ways. Sodium and potassium are both very reactive with water.
Complete this word equation: magnesium + hydrochloric acid → ______ + ______
Magnesium + hydrochloric acid → magnesium chloride + hydrogen.
Why does powdered magnesium react faster with acid than a strip of magnesium of the same mass?
The powder has a larger surface area exposed to the acid, so more collisions can occur and the reaction is faster.
Name one way to measure the pH of a substance.
Use universal indicator or pH paper and compare the colour with a pH colour chart.
Three metals are added separately to the same acid under the same conditions. Magnesium produces the most bubbles, zinc produces fewer, and copper produces none. Which metal is the least reactive, and what evidence supports your answer?
Copper is the least reactive of the three because it produces no bubbles, indicating that it does not react with the acid under these conditions.
An unknown element is a non-metal found in Group 7. Which group does it belong to, and what would you predict about its reactivity?
It belongs to the halogens. Halogens are reactive non-metals. They have similar chemical properties, although their reactivity varies.
A metal carbonate reacts with an acid. Name the three types of product formed and identify which one is a gas.
The products are a salt, water and carbon dioxide. Carbon dioxide is the gas.
What is a catalyst, and what happens to it during a chemical reaction?
A catalyst speeds up a chemical reaction and remains unchanged at the end.
What two products are formed when an acid is neutralised by an alkali?
Salt and water
A forensic scientist needs to identify whether an unknown soil sample is acidic, neutral or alkaline. Describe how they could test it.
Mix the soil with a suitable amount of distilled water, then test the resulting solution using pH paper or universal indicator. Compare the colour with the pH chart to classify it.
An unknown element conducts electricity and is found to the left of the zigzag line on the Periodic Table. Is it more likely to be a metal or a non-metal? Explain your answer and give one exception to the usual conductivity rule.
It is more likely to be a metal because metals generally conduct electricity and are found to the left of the zigzag line. Graphite, a form of carbon, is a non-metal that also conducts electricity.
A student reacts copper oxide with sulfuric acid. The products are copper sulfate and water. Write the complete word equation, then explain why copper sulfate has different properties from copper and sulfur.
Sulfuric acid + copper oxide → copper sulfate + water. Copper sulfate is a compound formed through chemical reactions; compounds can have very different properties from the elements that make them up.
A student investigates how temperature affects the rate of a reaction. Name the variable they should change, the variable they should measure, and one variable they should keep the same.
Change: temperature. Measure: reaction rate, such as the time taken to produce a set amount of gas. Keep the same: for example, the volume or concentration of acid, or the mass and particle size of the solid.
A student adds an acid to an alkaline solution. What happens to the pH as the alkali is neutralised, and why?
The pH decreases towards 7 because the solution becomes less alkaline. If enough acid is added, it may become acidic and the pH can fall below 7.
A student investigates how temperature affects the speed of a reaction. They use warmer acid and smaller pieces of metal in one experiment, but cooler acid and larger pieces in the other. Explain why the results would not be a fair comparison and how to improve the investigation.
Two variables have changed: temperature and particle size/surface area. The student should change only temperature while keeping the metal's mass, particle size, acid volume and concentration the same.