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SingaporeChemistryQuick questions
Stoichiometry and the Mole Concept
Quick questions on Chemical formulae and equations explained: O-Level Chemistry
7short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What are writing ionic formulae from charges?Show answer
An ionic compound is electrically neutral, so the total positive charge must equal the total negative charge. To write the formula:
What are balancing chemical equations?Show answer
A chemical equation must have the same number of atoms of each element on both sides, because atoms are not created or destroyed (conservation of mass). You balance by putting whole-number coefficients in front of the formulae. You may never change a formula (the subscripts) to balance, only the big numbers in front.
What is wrong state symbol for a dissolved substance?Show answer
A substance dissolved in water is , not .
What are not simplifying coefficients?Show answer
Reduce to the smallest whole-number ratio (for example divide all by if possible).
What is q1?Show answer
Write the formula of magnesium nitrate, given and . [2 marks]
What is q2?Show answer
Balance: . [2 marks]
What is q3?Show answer
State what state symbol is used for a substance dissolved in water, and give an example. [1 mark]
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