Block 2_chemistry B Pre-test

All of the above institutions employ scientists. Hospitals often employ medical scientists who conduct research and develop new treatments. Universities employ scientists in various fields to conduct research, teach, and mentor students. Corporations employ scientists in industries such as pharmaceuticals, technology, and energy to conduct research and development. Therefore, all of these institutions provide employment opportunities for scientists.

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 because broken glassware can be dangerous and may pose a risk to others in the lab. Following the teacher's instructions about proper clean-up and disposal of broken glassware is crucial to ensure the safety of everyone in the lab.

A scientific hypothesis is a testable assumption, meaning 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 substantial amount of evidence and has stood up to rigorous testing. It is used to explain a broad range of phenomena and is considered a more comprehensive and established explanation compared to a hypothesis. The answer accurately describes the key difference between a hypothesis and a theory in the scientific context.

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

JJ Thomson discovered the electron in his experiments. By passing electrical current through a cathode ray tube, he observed a beam of negatively charged particles moving from the cathode (negative electrode) towards the anode (positive electrode). These particles were later identified as electrons, which are subatomic particles with a negative charge. This discovery revolutionized our understanding of atomic structure and laid the foundation for the development of modern atomic theory.

Surface tension, capillary action, and high specific heat are all properties of liquid water that are 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" that allows insects to walk on water. Capillary action is the ability of water to move against gravity in narrow tubes, which is due to the adhesive forces between water molecules and the walls of the tube, as well as the cohesive forces between water molecules. High specific heat refers to the ability of water to absorb and retain heat, which is a result of the strong hydrogen bonding between water molecules that requires a lot of energy to break.

In the formation of a solution, the solute refers to the substance that is being dissolved. This means that it is the substance that is being added to the solvent and undergoes the process of dissolution. The solute can be a solid, liquid, or gas, depending on the nature of the solution. It is important to note that the solute is not always a solid substance, as it can also be a liquid or a gas that is being dissolved in a solvent.

An endothermic reaction is a reaction that absorbs thermal energy from its surroundings. This means that the surroundings gain thermal energy while the system loses it. In this case, the correct answer is "Thermal energy is absorbed by the surroundings," which accurately describes an endothermic reaction.

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 in the cylinder, and it is caused by the adhesive forces between the liquid and the cylinder. By looking at the bottom part of the meniscus, we can ensure that we are measuring the true volume of the liquid. The top part of the meniscus may appear higher due to surface tension, while averaging the top and bottom parts may lead to an inaccurate measurement. Ignoring the meniscus and simply determining which mL line the liquid is closest to would also result in an imprecise measurement.

A mole is a unit used to measure the amount of a substance. Avogadro's number states that one mole of any substance contains 6.02 x 10^23 representative particles, which can be atoms, molecules, or ions. Therefore, if we have a 2.50 mole sample, we can calculate the number of representative particles by multiplying the number of moles (2.50) by Avogadro's number (6.02 x 10^23). The result is 1.51 x 10^24, which represents the number of representative particles in the given sample.