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## Preparing for the Regent in Physics

Physics is a difficult class, usually taken in the junior year of high school. For NYC public school students, it is required to take a Regents exam at the end of the school year. So how can you best prepare for this test? You will need two books: Regents Exams and Answers: Physics (Barron's Regents NY), and Let's Review Physics: The Physical Setting. The second book is a review guide that covers all of the topics found on the Physics regent exam and has great practice questions at the end of each chapter. We suggest reviewing the topics and practicing the questions first. Once you feel like you have a solid understanding of the fundamentals, it is time to start with the heavy artillery. Th

## A photon with an energy of 1.33 × 10−21 joule has a frequency of

A photon with an energy of 1.33 × 10−21 joule has a frequency of (1) 5.02 × 10^13 Hz (2) 2.01 × 10^12 Hz (3) 8.82 × 10^14 Hz (4) 5.30 × 10^34 Hz Answer and Explanation: A photon is a particle of light. The formula for the energy of the photon can be found in the Physics Reference Table. It is Ephoton = hf where h is the plank's constant that can be found in reference table as well to be equal to 6.63 × 10–34 J•s. Therefore, all we need to do is plug in Planks constant as well as energy into the formula to find frequency. We get 1.33 × 10−21 = 6.63 × 10–34 J•s (f). F = 1.33 × 10−21/(6.63 × 10–34 J•s) = 2.006*10^12. Therefore, choice B is the correct answer. Transformation Tutoring has an amaz

## Le Chatelier's principle

Le Chatelier's principle says that when there is a stress on a system that takes it away from equilibrium, the system will react in such a way as to get back to the favorable equilibrium position. There are 4 stressors on the system. Lets list them and see what happens with each one. Lets say our equation is 2A (aq) + B(s) <---> C(g) 1. Concentration. When concentration is increased, equilibrium shifts to the opposite side to make up for it. For example, adding more A shifts the equilibrium to the right side, thus producing more C. When concentration is decreased, equilibrium shifts to the same side. Changes in solids and liquids DO NOT shift the equilibrium. 2. Pressure and volume. When

## Many disorders are due to the inability of an individual to break down a particular chemical.

Many disorders are due to the inability of an individual to break down a particular chemical. Sometimes these disorders can be treated by giving the affected individual the appropriate (1) enzymes (2) antigens (3) chromosomes (4) organelles Answer and explanation: There are many disorders where a person is unable to break down a chemical in the body, such as Phenylketonuria (PKU) (a person can not break down the amino acid phenylalanine). These conditions can be treated by giving the proper enzymes to an individual. Choice 1. Enzymes are biological catalysts that help to break down chemicals in our body. Therefore, if an individual is lacking the proper enzyme, he/she can be treated by recei

## AP Chem 2012 questions and answers (1-6)

(A) BeCl2 (B) SO2 (C) N2 (D) O2 (E) F2 Is a polar molecule. The easiest way to figure out whether a molecule is polar or non polar is to use these two principles: for a molecule to be nonpolar the central atom is surrounded by the sea atoms and has no lone pairs. Therefore, F2, O2, N2 are nonpolar (since its the same atoms connected to each other). BeCl2 is also nonpolar since beryllium is connected to two chlorines and has no lone pairs. Therefore, SO2 is polar, because sulfur has lone pairs on it. Choice B Is best represented by two or more resonance forms. Resonance forms are forms of the same molecule where electrons are moved and have a different location. Resonance forms can occur for

## 2018 AP Chemistry exam answers and explanations

The free response questions to the 2018 AP Chemistry can be founder here: https://apcentral.collegeboard.org/pdf/ap18-frq-chemistry.pdf?course=ap-chemistry Let's now understand the questions and how to answer them. 1. A student performs an experiment to determine the value of the enthalpy change, DH, for the oxidation-reduction reaction represented by the balanced equation above. (a) Determine the oxidation number of Cl in NaOCl. To determine the oxidation number, we first get all other oxidation numbers which are +1 for Na (group 1), and -2 for O (group 16). All of the charges must add up to zero in a neutral molecule. Therefore, we can make an equation of +1+x-2 = 0 x=+1, thus Cl has a -1

## Equivalence point for titrations

Titration is a lab technique where a known acid/base is added to unknown acid or base to find out its molarity. When stoichiometrically moles of acid are equal to moles of base, the equivalence point has been reached. A common question about the equivalence point is to find the pH of solution at that point. Let's break our titration into three categories. Strong acid with strong base titration: When a strong acid reacts with a strong base, water and neutral salt is created. The equivalence point of the strong acid/strong base titration has a pH of 7. Strong acid with weak base titration: When a strong acid reacts with weak base, water and acidic salt is produced. At equivalence point, all of

## Preparation for AP Chemistry exam.

AP Chemistry consists of the following topics: Structure of the atom, periodic table, ionic and covalent compounds, stoichiometry, gases, li

## TLC technique in organic chemistry lab

n the beginning of the procedure, the student puts a drop each of the control substances as well as experimental outcome. He/she then immers

## Grignard reagent in organic chemistry

Reactions of Grignard: Grignard reagent is a strong base. Thus it will attack any electrophile and can participate in a variety of reagents.

## How to determine whether salt is acidic, basic or neutral.

In general chemistry, semester 2, students learn about acids and bases. Salts are ionic compounds that are produced from the reaction of an acid with a base. Salts can be acidic, basic or neutral. How do we determine this? First, we must memorize all the strong acids which are:HCl - hydrochloric acid, HBr - hydrobromic acid, HI - hydroiodic acid, HNO3 - nitric acid, HClO3 - chloric acid, HClO4 - perchloric acid, H2SO4 - sulfuric acid. We have to also remember strong bases, which are group one and two with an OH (such as KOH, NaOH etc). Thus we can make 2 charts: Anions : Cl-, Br-, I-, NO3-, ClO3-, ClO4-, SO4 2- Cations: Group 1 & 2 (Ex: K+, Li+ ......) When looking at salt, if we cross out t

## Protein functional categories and digestion

Proteins are molecules built from amino acids. Proteins make up a large portion of our body and serve extremely important functions. These functions are: Enzymes - biological catalysts that speed up the rate of reactions in our body. Messengers - some hormones are proteins. Hormones are chemical messengers that are synthesized and secreted by endocrine tissues and target specific organs. Immunoproteins - provide protection to our body in the form of immunoglobulins and antibodies. Immunoglobulins are produced by white blood cells (plasma cells). These proteins bind to pathogenic cells, thereby targeting them for destruction. Buffers- many proteins serve as buffers, resisting pH changes and