Answer: To show the number of atoms present.
Explanation: As in CO² (Carbon dioxide), there is a small 2 next to the symbol "O" (oxygen) to explain that there are two oxygen atoms.
Water is not part of that compound. What is the chemical equation?
Answer: (2) decreasing the concentration of HCl(aq) to 0.1 M
Explanation: Rate of a reaction depends on following factors:
1. Size of the solute particles: If the reactant molecules are present in smaller size, surface of particles and decreasing the size increases the surface area of the solute particles. Hence, increasing the rate of a reaction.
2. Reactant concentration: The rate of the reaction is directly proportional to the concentration of reactants.
3. Temperature: Increasing the temperature increases the energy of the molecules and thus more molecules can react to give products and rate increases.
(1) Increasing the initial temperature to 25°C will increase the reaction rate.
(2) Decreasing the concentration of HCl(aq) to 0.1 M will decrease the reaction rate due to lesser concentration.
(3) Using 1.2 g of powdered Mg will increase the reaction rate due to large surface area.
(4) Using 2.4 g of Mg ribbon will increase the reaction rate due to high concentration of reactants.
For the first question, salt is soluble while sand is insoluble or not dissolvable in water. The salt should have vanished or melted, but the sand stayed noticeable or visible, making a dark brown solution probably with some sand particles caught on the walls of the container when the boiling water was put in to the mixture of salt and sand. The solubility of a chemical can be disturbed by temperature, and in the case of salt in water, the hot temperature of the boiling water enhanced the salt's capability to melt in it.
For the second question, the melted or dissolved salt should have easily made its way through the filter paper and into the second container, while the undissolved and muddy sand particles is caught on the filter paper. The size of the pores of the filter paper didn’t change. On the contrary, the size of the salt became smaller because it has been dissolved which is also the reason why it was able to go through the filter paper, while the size of the sand may have doubled or even tripled which made it harder to pass through.
