Pre-test Chemistry B Quiz Block 4

If a piece of laboratory glassware breaks, it is important for the student to immediately notify his/her teacher and students nearby of the broken glassware. This is necessary to ensure the safety of everyone in the lab and to prevent any injuries or accidents. The student should then follow the instructions given by the teacher about the proper clean-up and disposal of the broken glassware. This is important to prevent any further damage or harm and to maintain a safe environment in the laboratory.

All of the above institutions employ scientists. Hospitals often have research departments where scientists conduct medical research. Universities employ scientists as professors and researchers in various fields. Corporations, especially those in the pharmaceutical and technology industries, employ scientists for research and development purposes. Therefore, all three institutions mentioned employ scientists.

Melting butter is an example of a physical change because it involves a change in the state of matter from solid to liquid, without any change in the chemical composition of the substance. The molecules in the butter rearrange themselves when heated, causing it to change from a solid state to a liquid state. This change is reversible, as the melted butter can solidify again when cooled.

JJ Thomson discovered the electron. He passed electrical current through a cathode ray tube with positively charged plates at opposite ends and no air. He observed that a beam of particles, called cathode rays, moved from the negatively charged cathode towards the positively charged anode. This led him to conclude that these particles were negatively charged and much smaller than atoms, which he called electrons. This discovery revolutionized our understanding of atomic structure and laid the foundation for the development of modern physics.

A scientific hypothesis is a testable assumption, meaning that it can be experimentally or observationally tested to determine its validity. On the other hand, a scientific theory is a well-verified idea that has been supported by a significant amount of evidence and is used to explain a wide range of phenomena. The main difference between the two is that a hypothesis is a tentative explanation that is subject to testing and can be either supported or rejected, while a theory is a well-established and widely accepted explanation that has withstood rigorous testing and scrutiny.

An endothermic reaction is a reaction that absorbs thermal energy from its surroundings. This means that the surroundings will experience a decrease in temperature as the system absorbs heat. Therefore, the statement "Thermal energy is absorbed by the surroundings" accurately describes an endothermic reaction.

The properties of surface tension, capillary action, and high specific heat are all caused by water's intermolecular forces, specifically hydrogen bonds. Surface tension is the result of the cohesive forces between water molecules at the surface, which creates a "skin" or "film" on the surface. Capillary action is the ability of water to move against gravity in narrow spaces due to the adhesive forces between water and the surface of the container. High specific heat refers to water's ability to absorb and retain heat, which is due to the strong hydrogen bonding between water molecules that requires a large amount of energy to break. Therefore, all of these properties are influenced by water's intermolecular forces.

When measuring the volume of a liquid in a graduated cylinder, it is important to look at the bottom part of the meniscus. The meniscus is the curved surface of the liquid caused by capillary action. By looking at the bottom part of the meniscus, you are ensuring that the measurement is accurate and not affected by any distortion caused by the curved surface. This method allows for a more precise measurement of the liquid's volume.

In the formation of a solution, the solute is the substance that is being dissolved. When a solution is formed, one substance, called the solute, dissolves in another substance, called the solvent. The solute can be a solid, liquid, or gas, but in this case, it refers to the substance that is being dissolved.

A mole is a unit used to measure the amount of a substance. Avogadro's number, 6.02 x 10^23, represents the number of representative particles (atoms, molecules, or ions) in one mole of a substance. To find the number of representative particles in a 2.50 mole sample, we multiply the number of moles by Avogadro's number. Therefore, the correct answer is 2.50 x 10^23 x 6.02 x 10^23 = 1.51 x 10^24.