1. 5g of calcium is added to 100g of water in a beaker. the mass of the beaker at the end is less than 105g. explain why.
2. 5g of calcium oxide is added to 100g of water in a beaker. the mass of the beaker at the end is 105g. explain why it has not changed.
1. When calcium is added to water, it reacts with the water to form calcium hydroxide and hydrogen gas. The hydrogen gas is released into the air, reducing the mass of the beaker and its contents. Therefore, the mass of the beaker at the end is less than 105g.
2. When calcium oxide is added to water, it reacts with the water to form calcium hydroxide. This reaction does not release any gases, so the mass of the beaker and its contents remains the same at 105g.
1. The mass of the beaker at the end being less than 105g indicates that a chemical reaction has occurred between calcium and water. When calcium reacts with water, it forms calcium hydroxide (Ca(OH)2) and hydrogen gas (H2). The formation of these products leads to a decrease in the mass of the beaker since some of the reactants have been converted into new substances. The loss in mass can be attributed to the escape of hydrogen gas from the beaker, as it is a gaseous product and can easily leave the system.
2. In this case, the mass of the beaker at the end remaining at 105g suggests that no chemical reaction has taken place between calcium oxide and water. Calcium oxide (CaO) is a stable compound that does not react with water in a significant way. It is considered relatively inert or non-reactive when compared to calcium, as it does not readily undergo any noticeable reactions with water. Therefore, the mass of the beaker remains the same, indicating that there is no change in the total amount of matter present in the system.
1. When 5g of calcium is added to 100g of water in a beaker, the mass of the beaker at the end is less than 105g due to a chemical reaction called a displacement reaction. In this reaction, the calcium reacts with water to form calcium hydroxide (Ca(OH)2) and hydrogen gas (H2). The hydrogen gas is released into the air, causing a loss of mass.
To understand this, we need to look at the balanced chemical equation for the reaction:
Ca + 2H2O -> Ca(OH)2 + H2
From the equation, we can see that one mole of calcium (40g) reacts with two moles of water (36g) to produce one mole of calcium hydroxide (74g) and one mole of hydrogen gas (2g). The hydrogen gas is very light, and since it is released into the surrounding air, it causes a decrease in the overall mass of the system.
Therefore, the mass of the beaker at the end is less than 105g because some of the calcium has reacted with water, releasing hydrogen gas and reducing the total mass.
2. When 5g of calcium oxide (CaO) is added to 100g of water in a beaker, the mass of the beaker at the end is 105g and does not change significantly. This is because calcium oxide does not react with water in the same way as calcium.
Calcium oxide, also known as quicklime, is an ionic compound that is already fully oxidized. It does not undergo a displacement reaction with water but rather dissolves in water to form calcium hydroxide (Ca(OH)2). This process is called hydration.
The balanced equation for the reaction between calcium oxide and water is:
CaO + H2O -> Ca(OH)2
From the equation, we can see that one mole of calcium oxide (56g) reacts with one mole of water (18g) to produce one mole of calcium hydroxide (74g). The reaction between calcium oxide and water provides a sufficient mass to compensate for the small mass loss due to the dissolved calcium oxide.
Therefore, the mass of the beaker at the end remains relatively unchanged at 105g because the calcium oxide reacts with water to form calcium hydroxide, making up for any slight changes in mass.