Physical or Chemical?
What type of change occurs when no new substance is formed?
A physical change.
What do we call the substances present at the beginning of a chemical reaction?
Reactants.
What is the pH of a neutral solution?
pH 7.
What is the variable deliberately changed by the scientist?
The independent variable.
Which gas makes a squeaky pop when tested with a lighted splint?
Hydrogen.
Is cooking an egg a physical or chemical change? Explain briefly.
A chemical change, because new substances are formed.
What do we call the substances made during a chemical reaction?
Products.
What is the name of the reaction in which an acid is cancelled out by an alkali?
Neutralisation.
What is the variable that is measured or observed?
The dependent variable.
Which gas relights a glowing splint?
Oxygen.
Give three observations that may suggest a chemical reaction has occurred.
Any three: gas produced, colour change, temperature change, pH change, precipitate formed or reactant disappears.
Complete the word equation: magnesium + oxygen → ________.
Magnesium oxide.
Complete the general word equation: acid + alkali → ________ + ________.
Salt + water.
In an investigation comparing antacid powders, give two variables that should be kept the same.
Any two: volume of acid, type or concentration of acid, amount of indicator, spatula size, mixing method or neutral end point.
Which gas turns limewater cloudy or milky?
Carbon dioxide.
Chocolate melts when heated. Why is this normally classified as a physical change?
No new substance forms; only its state or shape changes.
Complete the word equation: zinc + hydrochloric acid → ________ + ________.
Zinc chloride + hydrogen.
Why should acid be added slowly from a burette while the mixture is swirled?
To mix each addition and avoid adding too much acid or passing the neutral point.
Why should an investigation be repeated, and why might a mean be calculated?
Repeats check consistency, improve reliability and help identify anomalies. A mean gives a representative value for comparison.
What is the scientific name for an insoluble solid that forms when two solutions react?
A precipitate.
Iron atoms bond with sulfur atoms to form iron sulfide. Explain why this is a chemical change using the idea of atoms.
The atoms are rearranged and chemically bonded into a new compound with different properties.
Why do bubbles during a metal-and-acid reaction not prove that the gas is hydrogen?
Bubbles only show that a gas formed. The gas must be identified using a gas test; hydrogen gives a squeaky pop with a lighted splint.
A student adds universal indicator to an acidic solution. They then add an alkali slowly. Describe the color change expected as the solution becomes neutral.
The indicator changes from an acidic color such as red, orange or yellow toward green at pH 7.
Three powders give these results for the number of spatulas needed: A = 7, 8, 7; B = 5, 9, 5; C = 6, 6, 6. Identify the anomalous result and the powder with the most consistent results.
The anomalous result is 9 for powder B. Powder C is the most consistent.
You have separate samples of hydrogen, oxygen, carbon dioxide and air. Describe how gas tests could identify all four.
Use separate samples. A lighted splint gives a pop with hydrogen. A glowing splint relights in oxygen. Carbon dioxide turns limewater cloudy. The sample that gives none of these positive results is air.