Review: solutions and metals
Last set. Litmus paper sorts solutions: acidic ones turn blue litmus red, alkaline ones turn red litmus blue, and neutral ones change neither. Lemon juice and vinegar are acidic, soapy water is alkaline, sugar water and salt water are neutral. When a solution evaporates, dissolved solids such as salt stay in the dish as crystals, but a dissolved gas, such as the carbon dioxide in sparkling water, escapes. Some metals bubble in a strong dilute acid, which gives off hydrogen. Afterwards, the dried solid is a new substance: dull, and it no longer bubbles. Gold stays bright because it does not react easily, and old metals can be recycled. In a lab we wear goggles, never taste, waft smells and tell the teacher about spills.
| Test | Result | Group or meaning |
|---|---|---|
| lemon juice on blue litmus | turns red | acidic |
| soapy water on red litmus | turns blue | alkaline |
| sugar water on both | no change | neutral |
| Metal | With dilute strong acid | Bright over time? |
|---|---|---|
| aluminium | bubbles | dull coating |
| iron | bubbles | rusts |
| gold | no reaction | stays bright |
Test card. Make a card for each of these words: acidic, alkaline, neutral, evaporate, new substance, recycle. On the back, write a one-line meaning and an example. Ask a family member to read a meaning so you can say the word.