Wednesday, September 20, 2006
Honors and Regents Chem Test Friday
Honors:
You will have a written test on the Matter and Energy unit. The test will be 5 to 8 written-response questions (no multiple choice); you will have 30 minutes for this exam though, on future exams, you will be allotted the whole period.
Experience from past classes has shown that most students do not know how to write an explanation. Also, some students do not yet use proper spelling and grammar. Spelling and grammar COUNT on all of the exams in this course! Go to the class webpage and download the file "Words that you are not allowed to misspell..." and write the words a hundred times if you have to because you will lose points each time you misspell those words. If you cannot express yourself clearly, you will not receive credit for your answers. You should have a decent command of English so that you may express yourself logically and unambiguously. My first writing tip: NEVER use pronouns in your answers. If you take the chance and you do use a pronoun that does not DEFINITELY refer to one and ONLY one noun in your sentence, then you will not receive credit for your unclear answer. So, be safe: avoid using pronouns unless and until you are expert at using them.
Here is a sample explanation to a question showing key features that are required in order to earn credit on any written exam in this course:
Explain the difference between the effect of a chemical change (reaction) and a physical change on the physical and chemical properties of substances. Give an example of each effect.
Answer:
(Start off by DIRECTLY answering what is asked for!) A chemical change will affect BOTH the physical and chemical properties of the substances that undergo the chemical change. For example, hydrogen and oxygen can undergo a chemical reaction (change) to form water. Water has different physical AND chemical properties than hydrogen and oxygen. With respect to physical properties, water is a liquid at room temperature whereas hydrogen and oxygen are not. Also, water is denser than either oxygen or hydrogen. With respect to chemical properties, water does not react/ combust with oxygen but hydrogen does react/combust with oxygen. Therefore, chemical change altered BOTH the physical and chemical properties of the reactants hydrogen and oxygen as they chemically combined to form water.
A physical change will ONLY affect the physical properties of a substance that undergoes the physical change. For example, MELTING is a physical change; when solid water melts to become liquid water, the chemical composition of water, H2O, does not change upon melting proving that a physical change, NOT a chemical change occurred. Liquid water has a different density than solid water (which is why ice cubes float on liquid water!), therefore, the physical property of density is altered as water undergoes a physical change. HOWEVER, liquid water and solid water have THE SAME chemical properties! They both do not react with oxygen, they both do react with sodium or potassium metal (as seen on the video on the class website). So, a physical change alters ONLY the physical properties of a substance but NOT the chemical properties of a substance.
Now THAT is a decent answer to a question because it
1. answers exactly what is asked for
2. provides specific supporting examples
3. concludes logically from the evidence and scientific definitions
One additional feature of most correct answers that I did not feature above is a LABELED DRAWING or ILLUSTRATION! Whenever possible, draw what you are describing or explaining FIRST! It is much easier to answer a question when you can refer to your drawing and/or draw arrows to the drawing indicating what you are describing.
Heed this advice before Friday and practice your written responses.
Regents: Though you will have a multiple-choice exam, you should heed the above advice for any test that you are taking in your classes. For your test, make sure that you understand any of the assigned hw questions / worksheets as well as anything from the notes/videos/powerpoints. Your exam will be between 25 and 33 questions.
You will have a written test on the Matter and Energy unit. The test will be 5 to 8 written-response questions (no multiple choice); you will have 30 minutes for this exam though, on future exams, you will be allotted the whole period.
Experience from past classes has shown that most students do not know how to write an explanation. Also, some students do not yet use proper spelling and grammar. Spelling and grammar COUNT on all of the exams in this course! Go to the class webpage and download the file "Words that you are not allowed to misspell..." and write the words a hundred times if you have to because you will lose points each time you misspell those words. If you cannot express yourself clearly, you will not receive credit for your answers. You should have a decent command of English so that you may express yourself logically and unambiguously. My first writing tip: NEVER use pronouns in your answers. If you take the chance and you do use a pronoun that does not DEFINITELY refer to one and ONLY one noun in your sentence, then you will not receive credit for your unclear answer. So, be safe: avoid using pronouns unless and until you are expert at using them.
Here is a sample explanation to a question showing key features that are required in order to earn credit on any written exam in this course:
Explain the difference between the effect of a chemical change (reaction) and a physical change on the physical and chemical properties of substances. Give an example of each effect.
Answer:
(Start off by DIRECTLY answering what is asked for!) A chemical change will affect BOTH the physical and chemical properties of the substances that undergo the chemical change. For example, hydrogen and oxygen can undergo a chemical reaction (change) to form water. Water has different physical AND chemical properties than hydrogen and oxygen. With respect to physical properties, water is a liquid at room temperature whereas hydrogen and oxygen are not. Also, water is denser than either oxygen or hydrogen. With respect to chemical properties, water does not react/ combust with oxygen but hydrogen does react/combust with oxygen. Therefore, chemical change altered BOTH the physical and chemical properties of the reactants hydrogen and oxygen as they chemically combined to form water.
A physical change will ONLY affect the physical properties of a substance that undergoes the physical change. For example, MELTING is a physical change; when solid water melts to become liquid water, the chemical composition of water, H2O, does not change upon melting proving that a physical change, NOT a chemical change occurred. Liquid water has a different density than solid water (which is why ice cubes float on liquid water!), therefore, the physical property of density is altered as water undergoes a physical change. HOWEVER, liquid water and solid water have THE SAME chemical properties! They both do not react with oxygen, they both do react with sodium or potassium metal (as seen on the video on the class website). So, a physical change alters ONLY the physical properties of a substance but NOT the chemical properties of a substance.
Now THAT is a decent answer to a question because it
1. answers exactly what is asked for
2. provides specific supporting examples
3. concludes logically from the evidence and scientific definitions
One additional feature of most correct answers that I did not feature above is a LABELED DRAWING or ILLUSTRATION! Whenever possible, draw what you are describing or explaining FIRST! It is much easier to answer a question when you can refer to your drawing and/or draw arrows to the drawing indicating what you are describing.
Heed this advice before Friday and practice your written responses.
Regents: Though you will have a multiple-choice exam, you should heed the above advice for any test that you are taking in your classes. For your test, make sure that you understand any of the assigned hw questions / worksheets as well as anything from the notes/videos/powerpoints. Your exam will be between 25 and 33 questions.
# posted by C @ 7:46 PM 
